Skeletal muscle voluntary
makes our bones move - biceps
Smooth muscle involuntary
takes care of processes we don't think about- action of the intestines (gut)
Cardiac muscle involuntary
- muscle that comprises the heart
Muscle
group of individual muscle cells with same attachments and function
Fascicles
bundles, CT covering on each one
Muscle fibers
muscle cells
Epimysium:
exterior collagen layer
connected to ___deep _____ fascia
Separates muscle from surrounding tissues
Perimysium:
surrounds muscle fiber bundles (fascicles)
contains blood vessel and nerve supply to fascicles
Endomysium:
surrounds individual muscle fibers
contains capillaries and nerve fibers contacting muscle cells
contains myosatellite cells (stem cells) that repair damage
tendon
bundles
aponeurosis
sheet
fibers
are muscle tissues
mesodermal cells (myoblasts)
Muscle fibers develop through the fusion of __________
sarcolemma
The cell ____membrane _______ of a muscle fiber (cell)
Surrounds the sarcoplasm (cytoplasm of muscle fiber)
A change in transmembrane potential begins contractions
Transverse tubules (T tubules
Transmit __action potential through cell
Allow entire muscle fiber to contract simultaneously
Have same properties as sarcolemma
Myofibrils
Lengthwise subdivisions within muscle fiber
Made up of bundles of protein filaments (myofilaments)
Myofilaments are responsible for muscle __conraction __
actin
thin filaments
myosin
thick filaments
Sarcoplasmic reticulum (SR)
A membranous structure surrounding each myofibril
Helps transmit action potential to myofibril
Similar in structure to smooth endoplasmic reticulum
Forms ___tubles______ (terminal cisternae) attached to T tubules
Triad
Is formed by __one___ T tubule and __two__ terminal cisternae
Cisternae:
concentrate Ca2+ (via ion pumps)
release Ca2+ into sarcomeres to begin muscle contraction
Contain calsequestrin - protein that reversibly binds Ca2+
Sarcomeres
The __contractile____________ units of muscle
Structural units of myofibrils
Form visible patterns within myofibrils
Muscle striations
A striped or striated pattern within myofibrils:
alternating dark, thick filaments (A bands) and light, thin filaments (I bands)
M line:
the center of the A band
at midline of sarcomere
, supporting proteins that hold the thick filaments together in the H zone, line of protein myomesin that holds adjacent thick filaments together
Z lines:
the centers of the I bands
at two ends of sarcomere
, boundaries of the sarcomere which give skeletal muscle its striated appearance,
Thin filament (thin horizontal lines), Thick filament (darker horizonal lines). From one z-line to another is one sarcome
Zone of overlap:
the densest, darkest area on a light micrograph
where thick and thin filaments overlap, think filaments are situated between thick filaments; in this region one thin filament is surrounded by three thick filaments, and each thick filament is surrounded by
The H Band:
the area around the M line
has thick filaments but no thin filaments, a band where only myosin molecules are found
Titin
are strands of ____protein reach from tips of thick filaments to the Z line
stabilize the filaments
, protein that connects m line to z line, maintains the position of the myosin in the center of the sarcomere and prevents the sarcomere from being pulled
Dystrophin
is a protein that was found to anchor the sarcomere to the sacolemma
muscular dystrophy
Defects or absence of this protein causes
F-actin (Filamentous actin)
Is two twisted rows of globular G-actin
The active sites on G-actin strands bind to myosin
Nebulin
Holds F-actin strands together
Tropomyosin
Is a double strand
Prevents actin-myosin interaction
Troponin
A globular protein
Binds tropomyosin to G-actin
Controlled by Ca2+
Thick Filaments
Contain twisted _msyosin________ subunits
Contain titin strands that recoil after stretching
The mysosin molecule
Tail:
binds to other myosin molecules
Head:
made of two globular protein subunits
reaches the nearest thin filament
Troponin-tropomyosin complex
helps to regulate contraction. this basically is what the actin myofilament is, strands of troponin and tropomyosin hence the complex. regulates interaction of active sites.
cross-bridges
myosin head, which connects thick filaments and thin filaments during a contraction
Interact with actin filaments, forming cross-bridges
Pivot, producing motion
active site
the specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.
Sliding filament theory
Thin filaments of sarcomere slide toward M line, alongside thick filaments
The width of A zone stays the same
Z lines move closer together
Contraction
formation of cross bridges between thin and thick filaments
excitation-contraction coupling
The mechanism that ensures tehat skeletal muscle contraction does not occur without neural stimulation (excitation). A trest, cytosolic [Calcium] is low, and the troponin, tropomyosin complex covers the myosin-binding sites on actin. When the muscle is st
tension
the action of stretching something tight
synaptic terminal
the location where axons terminate at the synapse for transmission of information by release of a chemical transmitter.
releases neurotransmitter (acetylcholine or ACh)
into the synaptic cleft (gap between synaptic terminal and motor end plate)
synaptic cleft
synaptic gap or synaptic space; tiny gap between the terminal of one neuron and the dendrites of another neuron (almost never touch); location of the transfer of an impulse from one neuron to the next
motor end plate
the flattened end of a motor neuron that transmits neural impulses to a muscle
The portion of the cell membrane at the neuromusclar junction; essentially the postsynaptic membrane at the synapse.
Acetylcholine
Travels across the synaptic _cleft_____
Binds to membrane receptors on sarcolemma (motor end plate)
Causes sodium-ion rush into sarcoplasm
Is quickly broken down by enzyme (acetylcholinesterase or AChE)
acetylcholinesterase
Enzyme that catalyzes breakdown of acetylcholine, preventing sustained muscle contraction from a single nerve impulse
excitation-contraction coupling
action potential reaches a triad:
releasing Ca2+
triggering contraction
requires myosin heads to be in "cocked" position:
loaded by ATP energy
, events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing
Sarcoplasmic reticulum
like smooth ER only flatter - stores calcium, The smooth ER of a muscle cell, enlarged and specialized to act as a Ca2+ reservoir. The SR winds around each myofibril in the muscle cell.
Sliding Filament Mechanism
Thick and thin filaments slide over eachother, myosin attches to actin and pulls thin filaments closer to the M line, each sarcomere shortens, but the length of the filaments doesn't change.
troponin
a regulatory protein that is a component of the thin filament. When calcium ions (Ca2+) bind to troponin, it undergoes a change in shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contractio
Troponin-tropomysin complex
Ca++ is essential for skeletal muscle contraction because it bonds with and removes the inhibitory effect of this.
Myosin heads
Bind to specific sites on actin molecules to form cross bridges
Relaxation
Ca2+ concentrations fall
Ca2+ detaches from troponin
Active sites are re-covered by tropomyosin
Sarcomeres remain contracted
, a method of solving simultaneous equations by guessing a solution and then reducing the errors that result by successive approxi
Rigor Mortis
A fixed muscular contraction after death
Caused when
Ion pumps cease to function; ran out of ATP
Calcium builds up in the sarcoplasm
, temporary stiffness of joints and muscular rigidity occurring after death
All-or-none principle:
Muscle cells are completely under the control of a motor neuron
Muscle cells cannot contract on their own
No half-hearted contraction for individual cell
Muscle cell cannot disobey an order
Always respond with a complete cycle contraction then relaxation
twitch
make an uncontrolled, short, jerky motion
Tension
of a Single Muscle Fiber is the stress resulting from the elongation of an elastic body.
Depends on
The number of pivoting cross-bridges
The fiber's resting length at the time of stimulation
The frequency of stimulation
Length-tension
relationship
Number of pivoting cross-bridges depends on:
amount of overlap between thick and thin fibers
Optimum overlap produces greatest amount of tension:
too much or too little reduces efficiency
Normal resting sarcomere length:
is 75% to 130% of opt
Latent period
before contraction
The action potential moves through sarcolemma
Causing Ca2+ release
Contraction phase
Calcium ions bind
Tension builds to peak
Relaxation phase
Ca2+ levels fall
Active sites are covered
Tension falls to resting levels
treppe
Motor unit stimulated immediately after complete relaxation. Force of contraction with increase due to increase in intracelluar Ca+.
A stair-step increase in twitch tension
Repeated stimulations immediately after relaxation phase
Stimulus frequency <50/se
Wave summation
Increasing tension or summation of twitches
Repeated stimulations before the end of relaxation phase:
stimulus frequency >50/second
Causes increasing tension or summation of twitches
Incomplete tetanus
Twitches reach maximum tension
If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension
Complete Tetanus
If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction
Myogram
The record or tracing produced by a myograph that measures and records the force of muscle contractions
Motor unit
smallest functional unit of contraction (all contracts at same time)
Made of:
Motor neuron - single cell
All of the muscle cells it controls
, one nerve fiber and all the muscle fibers innervated by it
Muscle tension
the amount of force a contracting muscle generates, Force exerted on an object by contracting or lengthening muscle
Recruitment (multiple motor unit summation)
In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated
Maximum tension
Achieved when all motor units reach tetanus
Can be sustained only a very short time
Sustained tension
Less than maximum tension
Allows motor units rest in rotation
Muscle tone
The normal tension and firmness of a muscle at rest
Muscle units actively maintain body position, without motion
Increasing muscle tone increases metabolic energy used, even at rest
Isotonic contractions:
muscle shortens, movement occurs - lifting your pencil
Isometric contractions
muscle doesn't shorten, no movement - lifting something that is too heavy & doesn't move - good way to strengthen muscle
Skeletal muscle develops tension, but is prevented from changing length
concentric contraction
A type of isotonic contraction that involves the muscle shortening while producing tension.
eccentric contraction
A type of isotonic contraction that involves the muscle lengthening while producing tension.
Resistance and Speed of Contraction
Are inversely related
The heavier the load (resistance) on a muscle
The longer it takes for shortening to begin
And the less the muscle will shorten
Muscle Relaxation
After contraction, a muscle fiber returns to resting length by
Elastic forces
Opposing muscle contractions
Gravity
Elastic Forces
The pull of elastic elements (tendons and ligaments)
Expands the sarcomeres to resting length
Opposing Muscle Contractions
Reverse the direction of the original motion
Are the work of opposing skeletal muscle pairs
Gravity
Can take the place of opposing muscle contraction to return a muscle to its resting state
Adenosine triphosphate
(ATP)
The active energy molecule
Creatine phosphate (CP)
The storage molecule for excess ATP energy in resting muscle
Energy recharges ADP to ATP
creatine phosphokinase
blood test to measure an enzyme of heart and skeletal muscle released into the blood following muscle injury or necrosis
Aerobic metabolism
Is the primary energy source of resting muscles
Breaks down fatty acids
Produces 34 ATP molecules per glucose molecule
Anaerobic glycolysis
Is the primary energy source for peak muscular activity
Produces two ATP molecules per molecule of glucose
Breaks down glucose from glycogen stored in skeletal muscles
Muscle Fatigue
inability of of a muscle to contract when stimulated caused by lack of oxygen, energy, and increased lactic acid
Depletion of metabolic reserves
Damage to sarcolemma and sarcoplasmic reticulum
Low pH (lactic acid)
Muscle exhaustion and pain
Recovery Period
The time required after exertion for muscles to return to normal
Oxygen becomes available
Mitochondrial activity resumes
The Cori Cycle
The removal and recycling of lactic acid by the liver (uses more ATP than is made)
Liver converts lactic acid to pyruvic acid
Glucose is released to recharge muscle glycogen reserves
Oxygen Debt
After exercise or other exertion
The body needs more oxygen than usual to normalize metabolic activities
Resulting in heavy breathing
Power
The maximum amount of tension produced, how fast u can run
Endurance
The amount of time an activity can be sustained
Power and endurance depend on
The types of muscle fibers
Physical conditioning
how far u can run
Intermediate fibers
Are mid-sized
Have low myoglobin
Have more capillaries than fast fibers, slower to fatigue
myoglobin
a hemoprotein that receives oxygen from hemoglobin and stores it in the tissues until needed
Slow twitch
endurance, red muscle, long duration contraction, contain myoglobin
Jogging, swimming, biking
, muscle fibers that work a long time without fatigue
Fast twitch:
strength, white muscle, short duration contraction
Sprinting, weight lifting, tennis
, muscle fibers that react quickly and fatigue quickly
White muscle
Mostly fast fibers
Pale (e.g., chicken breast, low in myoglobin, poor blood supply, fatique faster,operate anaerobically, used for short burst of activty
Red muscle
Mostly slow fibers
Dark (e.g., chicken legs)
, known as slow twitch muscle fibers: these fibers work constantly and have more oxygen
cardiocytes
cardiac muscle cells, smaller than skeletal muscle cells, are almost totally dependent on aerobic respiration.
Are small
Have a single nucleus
Have short, wide T tubules
Have no triads but have __Diad
Have SR with small terminal cisternae
Are aerobic (hig
Diads
In cardiac muscle, sarcoplasmic reticulum and t-tubules form ____ rather than triads found in skeletal muscle.
Intercalated Discs
Are specialized ___contacted points between cardiocytes
Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes)
Coordination of cardiocytes
Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart f
Functions of intercalated discs
Maintain structure
Enhance molecular and electrical connections
Conduct action potentials
Smooth Muscle Structure
__Nonstriated tissue
Different internal organization of actin and myosin
Different functional characteristics
, -spindle shaped with single central nucleus.
-walls of hollow organs (blood, vessels, GI tract, bladder)
-involuntary, unstriated
dense bodies
smooth muscle...thin filaments in smooth muscle are anchored directly to the sarcolemma or to protien muscles called _________
Excitation-contraction coupling
The events that occur between the time a nerve fiber stimulates a muscle fiber and the time the muscle fiber begins to contract are called _______________.
Free Ca2+ in ____Cytoplasm_ triggers contraction
Ca2+ binds with calmodulin:
in the sarcoplasm
acti
calmodulin
A cyoplasmic Ca2+-binding protein. Calmodulin is particularly important in smooth muscle cells, where binding of Ca2+ allows calmodulin to activate myosin light-chian kinase, the first step in smooth muscle cell contraction.
myosin light-chain kinase
phosphorylates the myosin head with ATP to bind actin creating the power stroke that slides thin filaments over thick filaments in smooth muscle contraction
Length-Tension Relationships
Thick and thin filaments are _scattered
Resting length not related to tension development
Functions over a wide range of lengths (plasticity)
plasticity
The ability of the brain to adapt to damage by reorganizing functions
Control of contractions
Multiunit smooth muscle cells:
connected to motor neurons
Visceral smooth muscle cells:
not connected to motor neurons
rhythmic cycles of activity controlled by pacesetter cells
Smooth muscle tone
Maintains normal levels of activity
__modified by:
neural,
hormonal, or
chemical factors
, a state of continued partial contraction that can sustain long-term tone in the GI tract and in the walls of blood vessels to maintain blood pressure
Parallel Muscles
Fibers _Parallel to the long axis of muscle
For example, biceps brachii
Depends on total number of myofibrils
Directly relates to cross section of muscle
1 in.2 (6.45 cm2) of cross section develops 50 lb (23 kg) of tension
, fibers parallel to the long ax
Convergent Muscles
A broad area _converge _on attachment site (tendon, aponeurosis, or raphe)
Muscle fibers pull in different directions, depending on stimulation
For example, pectoralis muscles
, broad area converges on attachment site (tendon, aponeurosis, or raphe); musc
Pennate Muscles
Form an ____Angle_ with the tendon
Do not move as far as parallel muscles
Contain more myofibrils than parallel muscles
Develop more tension than parallel muscles
, Muscles whose fibers run oblique to the long axis. Type I fiber muscles built for enduranc
Unipennate
Have muscle fibers that run obliquely to reach the tendon which is located along one edge
Fibers on one side of tendon
For example, extensor digitorum
Bipennate
Fibers on both sides of tendon
For example, rectus femoris
, In a _______ muscle, the fascicles diverge from both sides of a central tendon.
Multipennate
Tendon branches within muscle
For example, deltoid
, multi-tendons and multi-feathered. Deltoid.
Circular Muscles
Also called __sphincters
Open and close to guard entrances of body
For example, orbicularis oris muscle of the mouth
, thicken and shorten the muscles as they contract (worm squeezes up) attach setae to the soil as an anchor
Levers
Mechanically, each bone is a lever (a rigid, moving structure)
And each joint a fulcrum (a fixed point)
Muscles provide applied force (AF)
Required to overcome resistance (R)
fulcrum
the pivot point of a lever, the pivot about which a lever turns
applied force
muscles provide this to overcome resistance
First-Class Lever
Seesaw or teeter-totter is an example
Center fulcrum between applied force and resistance
Force and resistance are balanced
Second-Class Levers
Wheelbarrow is an example
Center resistance between applied force and fulcrum
A small force moves a large weight
Third-Class Levers
Most common levers in the body
Center applied force between resistance and fulcrum
Greater force moves smaller resistance
Maximizes speed and distance traveled
Origins and Insertions
Muscles have one __fixed______ point of attachment (origin) and one moving point of attachment (insertion)
Most muscles originate or insert on the skeleton
Origin is usually proximal to insertion
Muscle Actions
Movements produced by muscle contraction
Body movements
For example: flexion, extension, adduction, etc.
Described in terms of bone, joint, or region
Agonist(or prime mover)
a muscle that contracts while another relaxes
Produces a particular movement
Antagonist
a muscle that relaxes while another contracts
_opposes movement of a particular agonist
Synergist
A smaller muscle that assists a larger agonist
Helps start motion or stabilize origin of agonist (fixator), muscles that contract simultaneously with the prime mover to facilitate more effective movement(helps execute movement or steady a part)
Location in the Body
Identifies body regions
For example, temporalis muscle
Origin and Insertion
First part of name indicates origin
Second part of name indicates insertion
For example, coracobrachialis muscle
Fascicle Organization
Describes fascicle orientation within muscle
i.e., rectus (straight), transversus, oblique
Relative Position
Externus (superficialis)
Visible at body surface
Internus (profundus)
Deep muscles
Extrinsic
Muscles outside an organ
Intrinsic
Muscles inside an organ
Action
Movements
For example, flexor, extensor, retractor
Occupations or habits
For example, risor = laughter
Hindbrain
coordinates basic, automatic, vital functions
Medulla oblongata:
controls automatic functions of internal organs
Cerebellum:
coordinates basic movements
Midbrain:
coordinates muscles related to vision & hearing
Forebrain
: receives and integrates information concerning emotions and conscious thought
Thalamus
receiving, processing, and transfer center
Cerebrum/cerebral cortex
higher functions
Compartment Syndrome
Muscle groups are isolated in compartments
Swelling can injure all structures of a given compartment
Strength training
Resistance training
Short, intense
Specific muscles
Builds more fast-twitch myofibrils
Aerobic training
Builds ____endurance
Increases blood supply to muscle cells
Target heart rate at least 20 minutes, three times a week
Increases number of mitochondria & myoglobin
Cardiovascular & respiratory systems
afferent
Division of the Nervous System
Receptors
Sensory neurons
Sensory pathways
efferent
Division of the Nervous System
Nuclei
Motor tracts
Motor neurons
Sensory Receptors
Specialized cells that monitor specific conditions in the body or external environment
When stimulated, a receptor passes information to the CNS in the form of action potentials along the axon of a sensory neuron
Sensory Pathways
Deliver somatic and visceral sensory information to their final destinations inside the CNS using
Nerves
Nuclei
Tracts
Somatic Motor Portion
Controls peripheral effectors
Somatic Motor Commands
Travel from __motor______ centers in the brain along somatic motor pathways of
Motor nuclei
Tracts
Nerves
Somatic Nervous System
Motor neurons and pathways that control skeletal muscles
Mechanoreceptors
respond to mechanical energy
Thermoreceptors
respond to temperature, hot or cold
Pain Receptors
respond to tissue injury, excessive pressure
Chemoreceptors:
respond to the presence of chemicals; taste and smell
Photoreceptors:
respond to light (special sense only)
Receptor sensitivity
Each receptor has a characteristic sensitivity
Receptive field
Area is monitored by a _single __ receptor cell
The larger the receptive field, the more difficult it is to localize a stimulus
Arriving stimulus
Takes many forms:
physical force (such as pressure)
dissolved chemical
sound
light
Sensations
Taste, hearing, equilibrium, and vision provided by specialized receptor cells
Communicate with sensory neurons across chemical synapses
Adaptation
Reduction in __sensitivity___________ of a constant stimulus
Your nervous system quickly adapts to stimuli that are painless and constant
Types:
Tonic Receptors
Phasic Receptors
Tonic receptors
Are ___always_______ active
Show little peripheral adaptation
Are slow-adapting receptors
Remind you of an injury long after the initial damage has occurred
slow-adapting receptors
Receptors that continue to respond for long periods of time with continuous stimulation.
Phasic receptors
Are normally inactive
Become __active________ for a short time whenever a change occurs
Provide information about the intensity and rate of change of a stimulus
Are fast-adapting receptors
fast-adapting receptors
Adaptation that results from synaptic fatigue, like that which occurs when you get used to the water temperature in the shower, is a property of:
Exteroceptors
provide information about the external environment, These receptors are located in the skin and give information on pain, temperature, pressure, touch
Proprioceptors
report the positions of skeletal muscles and joints, Sensory receptors, located in the muscles and joints, that provide information about body position and movement.
Interoceptors
monitor visceral organs and functions, monitor digestive, respiratory, cardiovascular, urinary, and reproductive systems
Nociceptors (also called __pain _ receptors)
Are common in the superficial portions of the skin, joint capsules, within the periostea of bones, and around the walls of blood vessels
May be sensitive to temperature extremes, mechanical damage, and dissolved chemicals, such as chemicals released by in
free nerve endings
Branching tips of dendrites
Not protected by accessory structures
Can be stimulated by many different stimuli
Two types of axons:
Type A fibers
Type C fibers
Myelinated Type A fibers
Carry sensations of _fast_____ pain, or prickling pain, such as that caused by an injection or a deep cut
Sensations reach the CNS quickly and often trigger somatic reflexes
Relayed to the primary sensory cortex and receive conscious attention
Type C fibers
Carry sensations of ___slow___ pain, or burning and aching pain
Cause a generalized activation of the reticular formation and thalamus
You become aware of the pain but only have a general idea of the area affected
Thermoreceptors
Also called temperature receptors
Are free nerve endings located in
The dermis
Skeletal muscles
The liver
The hypothalamus
Chemoreceptors
Respond only to water-soluble and lipid-soluble substances dissolved in surrounding fluid
Receptors exhibit peripheral adaptation over period of seconds; central adaptation may also occur
central adaptation
adaptation that involves inhibition along the sensory pathways
_carotid bodies
near the origin of the internal carotid arteries on each side of the neck
Aortic bodies:
between the major branches of the aortic arch
Receptors monitor pH, carbon dioxide, and oxygen levels in arterial blood
Mechanoreceptors
Sensitive to ___stimuli______ that distort their plasma membranes
Contain mechanically gated ion channels whose gates open or close in response to
Stretching
Compression
Twisting
Other distortions of the membrane
Baroreceptors
Detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts
Proprioceptors
Provide a purely somatic sensation
No proprioceptors in the visceral organs of the thoracic and abdominopelvic cavities
You cannot tell where your spleen, appendix, or pancreas is at the moment
Muscle spindles
Monitor skeletal muscle length
Trigger stretch reflexes
Golgi tendon organs
Located at the junction between skeletal muscle and its tendon
Stimulated by tension in tendon
Monitor external tension developed during muscle contraction
Receptors in joint capsules
Free nerve endings detect pressure, tension, movement at the joint
Tactile Receptors
provide the sensations of touch, pressure, and vibration:
touch sensations provide information about shape or texture
pressure sensations indicate degree of mechanical distortion
vibration sensations indicate pulsing or oscillating pressure
Fine touch and pressure receptors
Are extremely ___sensitive_________
Have a relatively narrow receptive field
Provide detailed information about a source of stimulation, including:
its exact location, shape, size, texture, movement
Crude touch and pressure receptors
Have relatively __larger ______ receptive fields
Provide poor localization
Give little information about the stimulus
Free nerve endings
Sensitive to touch and pressure
Situated between epidermal cells
Free nerve endings providing touch sensations are tonic receptors with small receptive fields
Root hair plexus nerve endings
Monitor distortions and movements across the body surface wherever hairs are located
Adapt rapidly, so are best at detecting initial contact and subsequent movements
Tactile discs
Also called __Merkel discs_ discs
Fine touch and pressure receptors
Extremely sensitive to tonic receptors
Have very small receptive fields
Tactile corpuscles:
Also called ____Meissner _ corpuscles
Perceive sensations of fine touch, pressure, and low-frequency vibration
Adapt to stimulation within 1 second after contact
Fairly large structures
Most abundant in the eyelids, lips, fingertips, nipples, and external
Lamellated corpuscles
Also called ___Pacinian_ corpuscles
Sensitive to deep pressure
Fast-adapting receptors
Most sensitive to pulsing or high-frequency vibrating stimuli
Ruffini corpuscles
Also sensitive to pressure and distortion of the skin
Located in the reticular (deep) dermis
Tonic receptors that show little if any adaptation
Neurons
: specialized cells for communication
Types of neurons
Sensory afferent
__Interneurons__
Motor neurons
First-Order Neuron
Sensory neuron delivers sensations to the CNS
Cell body of a first-order general sensory neuron is located in dorsal root ganglion or cranial nerve ganglion
Second-Order Neuron
Axon of the sensory neuron synapses on an __interneurons_ in the CNS
May be located in the spinal cord or brain stem
Third-Order Neuron
If the sensation is to reach our awareness, the second-order neuron synapses on a third-order neuron in the thalamus
Sensory homunculus
Functional __map____ of the primary sensory cortex
Distortions occur because area of sensory cortex devoted to particular body region is not proportional to region's size, but to number of sensory receptors it contains
Posterior column pathway
Carries __sensation _______ of highly localized ("fine") touch, pressure, vibration, and proprioception
Spinal tracts involved:
left and right fasciculus gracilis
left and right fasciculus cuneatus
The Spinothalamic Pathway
Provides conscious __sensation_ of poorly localized ("crude") touch, pressure, pain, and temperature
First-order neurons
Axons of first-order sensory neurons enter spinal cord and synapse on second-order neurons within posterior gray horns
spinothalamic tracts:
the anterior tracts carry crude touch and pressure sensations
the lateral tracts carry pain and temperature sensations
referred pain
Activity in interneurons leads to stimulation of primary sensory cortex, so an individual feels pain in specific part of body surface:
, pain felt at a particular site, but originates from another location
The pain of a heart attack is frequently felt in
The Spinocerebellar Pathway
Cerebellum receives _propricoceptive information about position of skeletal muscles, tendons, and joints
posterior spinocerebellar tracts
Contain second-order axons that do _NOT_____ cross over to the opposite side of the spinal cord:
axons reach cerebellar cortex via inferior cerebellar peduncle of that side
The anterior spinocerebellar tracts
Dominated by second-order axons that have crossed over to opposite side of spinal cord
Contain significant number of uncrossed axons as well:
sensations reach the cerebellar cortex via superior cerebellar peduncle
many axons that cross over and ascend to
Visceral Sensory Pathways
Collected by interoceptors monitoring __visceral______ tissues and organs, primarily within the thoracic and abdominopelvic cavities
These interoceptors are not as numerous as in somatic tissues
Nociceptors, thermoreceptors, tactile receptors, barorecepto
_Solitary __ nucleus
Large nucleus in the medulla oblongata
Major processing and sorting center for visceral sensory information
Extensive connections with the various cardiovascular and respiratory centers, reticular formation
SNS,
or the somatic motor system, controls contractions of skeletal muscles (discussed next)
ANS,
or the visceral motor system, controls visceral effectors, such as smooth muscle, cardiac muscle, and glands (Ch. 16)
somatic motor neurons Upper motor neuron
Cell body lies in a CNS processing center
Synapses on the lower motor neuron
Innervates a single motor unit in a skeletal muscle:
activity in upper motor neuron may facilitate or inhibit lower motor neuron
somatic motor neurons Lower motor neuron
Cell body lies in a nucleus of the brain stem or spinal cord
Triggers a contraction in innervated muscle:
only axon of lower motor neuron extends outside CNS
destruction of or damage to lower motor neuron eliminates voluntary and reflex control over inner
Corticospinal Pathway
Sometimes called the ____pyramidal __ system
Provides voluntary control over skeletal muscles
System begins at pyramidal cells of primary motor cortex
Axons of these upper motor neurons descend into brain stem and spinal cord to synapse on lower motor neu
Corticobulbar tracts
Provide conscious control over skeletal muscles that move the eye, jaw, face, and some muscles of neck and pharynx
Innervate motor centers of medial and lateral pathways
Use the motor nuclei of cranial nerves
Corticospinal tracts
As they descend, lateral corticospinal tracts are visible along the ventral surface of medulla oblongata as pair of thick bands, the pyramids
At spinal segment it targets, an axon in anterior corticospinal tract crosses over to opposite side of spinal cor
Motor homunculus
Primary motor cortex corresponds point by point with specific regions of the body
Cortical areas have been mapped out in diagrammatic form
__Homunculus_ provides indication of degree of fine motor control available:
hands, face, and tongue, which are capa
The Medial and Lateral Pathways
Several centers in cerebrum, diencephalon, and brain stem may issue somatic motor commands as result of processing performed at subconscious level
medial pathway
help control ___gross_____ movements of trunk and proximal limb muscles
lateral pathway
help control distal limb muscles that perform more precise movements
Vestibular nuclei
Receive information over the vestibulocochlear nerve (VIII) from receptors in inner ear that monitor position and movement of the head:
primary goal is to maintain posture and balance
descending fibers of spinal cord constitute vestibulospinal tracts
Superior and inferior colliculi
Are located in the roof of the mesencephalon, or the __tectun___
Colliculi receive visual (superior) and auditory (inferior) sensations
Axons of upper motor neurons in colliculi descend in tectospinal tracts
These axons cross to opposite side, before desc
Reticular formation
Loosely organized network of neurons that extends throughout brain stem
Axons of upper motor neurons in reticular formation descend into reticulospinal tracts without crossing to opposite side
The Lateral Pathway
Primarily concerned with control of muscle tone and more __precise movements of distal parts of limbs:
axons of upper motor neurons in red nuclei cross to opposite side of brain and descend into spinal cord in rubrospinal tracts
The Basal Nuclei
Provide background patterns of movement involved in voluntary motor activities
Some axons extend to the premotor cortex, the motor association area that directs activities of the primary motor cortex:
alters the __pattern__________ of instructions carried
Cerebellum
Monitors
Proprioceptive (position) sensations
Visual information from the eyes
Vestibular (balance) sensations from inner ear as movements are under way