Nervous system
Nervous system is responsible for remembering, movements, feeling, thinking, sensations, etcprimary coordinating and controlling system of the body - info from outside & inside the body causes changes inside body (maintain homeostasis)
Anatomical divisions
Central nervous system (CNS)Peripheral Nervous System (PNS)
Central Nervous System
Brain and Spinal Cord
Peripheral Nervous System
Consists of cranial nerves and spinal nerves, outside the CNS, consists of receptors and effectors
Functional divisions
Sensory divisionMotor division
Sensory division
Carries impulses from sensory receptors to the CNS
Impulse
electrochemical signal that allows neurons to communicate
Motor division
Carries impulses from CNS out to effectors (muscles & glands),Somatic nervous system, autonomic nervous system
Somatic nervous system
Voluntary control of skeletal muscle, connects CNS to skin, motor functions; conscious activitesincludes only a single neuron between CNS and skeletal muscle
Autonomic nervous system
Involuntary control of cardiac muscle, smooth muscle, and glands, connect CNS to viscera, motor functions; subconscious activites, Purpose is to maintain homeostasis in response to changes in internal conditions (ex: emotional stress)only motor fibers
Autonomic nervous system organization
Preganglionic neuron Postganglionic neuron
Preganglionic neuron
extends from CNS to autonomic ganglion in PNS
Postganglionic neuron
extends from autonomic ganglion to visceral effector (cardiac muscle, smooth muscle, or gland)
Autonomic nervous system divison
sympathetic, parasympathetic
Sympathetic division
Preganglionic axons exit the spinal cord at thoracic and lumbar regions (T1-L2) and enter a chain of sympathetic gangliaparavertebral gangliaPreganglionic fibers release Ach - called "cholinergic"Postganglionic fibers release norepinephrine - called "adrenergic"sweat glands and blood vessels- sympathetic input only sympatheticFight or flight, increases heart rate/decreases digestion, increases blood supply to sketetal/ decreases to digestive, dilates bronchioles
paravertebral ganglia
Chain extends longitudinally along each side of the spine, can be long postsynaptic fiber
Parasympathetic Division
Preganglionic fibers emerge from brain stem and sacral region of spinal cord (S2-S4)Synapse with postganglionic neurons in ganglia close located to visceral organsBoth preganglionic and postganglionic fibers are cholinergicRest and digest, decreases heart rate/ increases digestion, decreases blood supply to skeletal, increases to digestive, constricts bronchioles
General steps of neurotransmission
1. Sensory nerves detect internal and external changes2. Sensory nerves send information to central nervous system 3. Organization and interpretation of information in CNS - "integration" (translate sensations into perceptions) 4. Initiation of appropriate action - can be conscious or subconscious; usually a motor nerves initiates a motor function
neurons
nerve cells, transmit neural impulses, pass info at synapse
Structure of a neuron
cell body/somadendritesaxon/nerve fibermyelin sheath
Cell body/soma
has nucleus and organelles
Dendrites
Numerous, short, highly branched processes that extend from cell body, Receive impulses; carry impulses toward cell body
Axon/nerve fiber
Long, thin process, Ends in axon terminals with synaptic knobs, Carry impulses away from cell body
myelin sheath
insulates axons & increases speed of impulse transmission
Nodes of Ranvier
gaps between myelinated areas
Types of Neurons
Sensory neurons (afferent), Interneurons (association), Motor neurons (efferent)- Carry impulses from CNS to effectors
Sensory neurons (afferent)
Effectors- ex. Muscles, glands,Carry impulses from PNS to the CNS, Detect changes directly (on ends of dendrites) or via sensory receptors in the skin & sense organs, ganglia
Ganglia
cell bodies grouped in masses in the PNS, sensory neurons
Interneurons (association)
Process and interpret impulses in CNS, Send impulse to proper area of brain for processing or will activate motor neurons, nuclei
Nuclei
cell bodies grouped in masses in the CNS, interneurons
Motor neurons (efferent)
Carry impulses from CNS to effectors to produce an actionCell bodies and dendrites are in CNSAxon is located in nerves of PNS
Neuroglia (glia/glial)
cells that support and protect neurons
Synaptic transmission
1. Arrival of an impulse causes synaptic knob to release a neurotransmitter (chemical signal molecule) into the synaptic cleft2. Neurotransmitters bind to receptors on postsynaptic cell's plasma membrane3. A response is triggered in the postsynaptic cell4. Stimulates impulse formation OR inhibits impulse formation in postsynaptic cell
Synapse
Junction of an axon with another neuron or an effector cell
Synapse structure
1. Synaptic knob of presynaptic neuron2. Postsynaptic cell (neuron or effector)3. Synaptic cleft
Synaptic cleft
Space between presynaptic knob & postsynaptic cell
Two basic types of neurotransmitters
excitatory, inhibitory
Excitatory
Cause impulse formation in postsynaptic neuron and activate other cellsExamples: acetylcholine, epinephrine-fight or flight
Inhibitory
Inhibit the formation of impulses in postsynaptic cells and function of other target cellsExamples: GABA, endorphins, serotonin
Resting Membrane Potential
Membrane is polarized due to an unequal distribution of electrical charges on each side of the plasma membrane
Resting Membrane Potential
1. positively charged ions outside (Na+ ) membrane2. negatively charge ions on the inside of the neuron membrane (less K+, PO4-3, and SO4-2 )3. At rest, pumps in the cell membrane actively transport Na+ and K+ in opposite directions to maintain resting potential (-70mV)
Impulse/ Action Potential formation
When activated by a stimulus:1. Na+ channels open and Na+ rushes into the neuron 2. Causes the inside of the membrane to become more positive - depolarizedA stimulus must be strong enough to actually cause depolarization to happen
Threshold potential
caused by a sufficient stimulus frequency, results in an action potential
All impulses are alike
not stronger or weaker, iii. increased intensity of a stimulus produces more impulses per second (increased freq), not stronger impulse
Repolarization
After depolarization, K+ diffuses outward to re-establish the membrane potentialNa+ is then pumped out and K+ is pumped in to reestablish resting-state ion distribution
Impulse conduction
Depolarization at one point triggers depolarization in adjacent portions, etc.
Impulse conduction
1. Forms a wave of depolarization sweeping along the neuron, Spreading of the impulse down the membrane2. More rapid in myelinated neurons than unmyelinated neurons i. Impulses skip from nodes to node ii. Impulse travels faster along i. axon with larger diameter (ex: motor neuron in skeletal muscle - 120m/sec vs. unmyelinated sensory neuron in skin - .5m/sec)
Meninges
membranes that cover the brain & spinal cordDura mater, Arachnoid mater, Pia mater
Dura mater
Tough and fibrous; outermost layerAttached to cranial bones; many blood vessels and nervesCan extend inwards with folds of cerebrumDura mater provides outer most layer of protect for spinal cord - not attached to vertebrae however creating epidural space
epidural space
space between dura mater and vertebrae
Arachnoid mater
Thin; web-like middle layeradheres tightly to brain; no blood vessels Subarachnoid space
Subarachnoid space
between arachnoid & pia; filled with cerebrospinal fluid (CSF)
Pia mater
Thin; innermost layerAdheres to CNS surfacesContains nerves & blood vessels to nourish brain and spinal cord
What is Meningitis??
Inflammation of the meninges, can be passed among a large group of people
Brain
Cerebrum, Cerebellum, Diencephalon, Brain Stem
Cerebrum
higher mental functions (memory, reasoning); sensory, motor functions
Cerebrum structure
Left and right cerebral hemispheresseparated by longitudinal fissureconnected by corpus callosumgyri and suclicerebral cortexwhite matterFrontal lobe, parietal lobe, temporal lobe, occipital lobe
gyri
folds
sulci
shallow grooves
Cerebral cortex
Outer surface of gray matter, contains 75% of neuron cell bodies, unmyelinated
White matter
majority of cerebrum, myelinated fibers that transmit impulses, contain nuclei
Functional areas of cerebrum
sensory areas (cutaneous, visual, auditory, gustatory, olfactory) motor areas-located in frontal lobe (primary motor, broca's area, frontal eye field area)association areas-located in each lobe, connect sensory and motor (Wernicke's)
Cutaneous Sensory Area
parietal lobe; interprets sensations from skin
Visual Area
occipital lobe; interprets vision
Auditory Area
temporal lobe; interprets hearing
Sensory Area for Taste (gustatory)
parietal cortex, just above temporal lobe; interprets impulses from taste buds
Sensory Area for Smell (olfactory)
arise from centers deep within the cerebrum; interprets smells
Primary motor area
controls skeletal musclesLeft side of the cerebrum controls skeletal muscles on the right side of the body (axons cross over in brainstem)
Broca's area
controls muscles needed to speak (only on left side)
Frontal eye field area
controls voluntary eye movements
Wernicke's area
L hemisphere; ability to understand written/spoken language
Cerebellum
coordinates muscular activities, controls posture, balance, and muscle coordination, grey and white matter
Diencephalon
processes sensory input, lies between cerebral hemispheres and midbrain, thalamus, hypothalamus, control for autonomic nervous system
Thalamus
receives all sensory impulses (except smell) and sends them to respective cerebral area for processing; "information filter"general nonspecific awareness of sensations (pain, touch, temp)
Hypothalamus
major regulator of homeostasis!Produces hormones to be secreted by pituitary gland (endocrine system)Because hypothalamus controls pituitary gland, nervous and endocrine systems are connected - ex: stress responseHormone released from hypothalamus to pituitary gland to adrenal glands (on kidney) that signals to release cortisol
Limbic system
Clusters of nuclei (grey matter) deep in cerebrum, Controls emotional experiences and expression (produces feelings)
Basal nuclei
produce inhibitory neurotransmitter dopamineThese neurons interact with limbic system portion of brain to facilitate movement Most addictive drugs or behaviors become addictive by modulating this pathway
Brain stem
coordinates & regulates visceral activities, connects cerebrum and spinal cord, midbrain, pons, medulla oblongata
Midbrain
reflex center for visual and auditory stimuli
Pons
Aids in controlling the rate and depth of breathingbetween midbrain and medulla oblongataRelay sensory impulses from PNS to brain
Medulla oblongata
Controls reflexes like coughing, sneezing, swallowing & vomitingMost inferior portion of the brain that connects to the spinal cordRespiratory control center, cardiac control center, vasomotor centerreceives impulses from Vagus Nerve
respiratory control center
regulates breathing rhythm; adjust depth and rate of breathing
cardiac control center
Regulate rate of heart contractions
vasomotor center
Regulates blood pressure and blood flow
Reticular formation
Network of nerves and grey matters in brain stem and spinal cordImpulses to this area promote wakefulness in the cerebrum- without cerebral cortex is unaware of stimulation
Ventricles
hollow cavities filled with cerebrospinal fluid
cerebrospinal fluid
Nourishes the CNS tissues, maintains ion balances, & protects by absorbing shockCSF circulates around the brain, also provides way for wastes to exit to blood
What is a spinal tap?
Measures the pressure of Cerebrospinal fluid
Spinal Cord
Transmit impulses to and from brain Reflex center for spinal reflexesDescends from medulla oblongata through foramen magnum Passes through vertebral canal to level of 2nd lumbar vertebra; only spinal nerves extend past this part
Spinal cord structure
1. cervical & lumbar enlargements2. conus medullaris3. cauda equine4. dorsal (sensory) & ventral (motor) roots
Spinal nerves
31 pairs of mixed nerves branching off of the spinal cord a. 8 pairs of cervical nerves (only 7 cervical vertebra - C1 emerges above atlas) b. 12 pairs of thoracic nervesc. 5 pairs of lumbar nervesd. 5 pairs of sacral nervese. 1 pair of coccygeal nerves
Plexuses
networks of nerves A plexus is a made of merged anterior branches from several nervesAxons from different spinal nerves are combined and extend to the same body part Cervical, Brachial, Lumbosacral
Cervical
C1-C4Nerves from it go to muscles and skin of neck, head, and shouldersEx: phrenic nerves - motor impulses to diaphragm
Brachial
C5-T1Nerves go to skin and muscles of arms and shouldersEx: radial & ulnar
Lumbosacral
L1-S4Nerves from it supply skin and muscles of lower trunk, genitalia, buttocks, thighs, feetEx: femoral and obturator
2 main subdivisions of PNS
Somatic, AutonomicBoth divisions consist of cranial nerves and spinal nerves
Motor nerves
axons of motor neurons
Sensory nerves
axons of sensory neurons
Mixed nerves
contain both
Cortisol production
Hypothalamus to release Corticotropin releasing hormone (CTH) targets the pituitary to release adrenocorticotropic hormone (ACTH)targets the adrenal gland to release cortisol → targets cells to release energy substratesAcute stress causes increased sympathetic nervous sys activityEpinephrine & Norepinephrine are made by the adrenal gland
Negative Feedback
releases and inhibits hormones, causes them to fluctuation throughout the day
Long term stress
blood concentration of amino acids increasesrelease of fatty acids increasesglucose formed from noncarbohydrates-amino acids(from proteins) and glycerol(from fats)-increases
Sensation
when sensory receptors are stimulated and reach threshold (generating an action potential), the brain becomes aware of the stimulusIntensity of the sensation depends upon frequency of impulses
Frequency of impulses
Greater frequency of impulses means greater intensity of sensation AND greater stimulus intensity means greater frequency of impulsesEx: drink with ↑ conc. of sugar = ↑ freq of AP generated = ↑ perception of sweetness
Perception
a person's "experience" of the stimulus; the way the brain interprets the sensationPain = sensation; realization of stepping on tack = perception
Projection
Cerebral cortex projects the sensation back to the body region where the impulses originated allows you to know the origin of the sensation → this is how the eyes "see", ears "hear", etc!
Adaptation
Decline in the rate of impulse formation due to repeated stimulation by the same stimulusEx. Smelling your own perfume/cologne All receptors except pain receptors adapt
General Senses
receptors are spread throughout the body (pain, touch, pressure, cold, and heat)Thermoreceptors, Mechanoreceptors, pain receptors
Thermoreceptors
adapt quickly, free nerve endings in the skin are stimulated by temp. changes
Mechanoreceptors
Sensitive to mechanical stimuli that displaces the tissue surrounding the receptor (pressure & touch)
Pain Receptors
free nerve endings widely distributed throughout the skin & internal tissues (except the brain - none)Stimulated by tissue damageReceptors adapt slowly or not at all
Referred pain
Pain impulses originate from visceral organs but is felt somewhere else in the body Pain is projected along common nerves pathways
What is Angina?
Not enough blood flow to your heart tissue, pain is felt through the left arm
Regulation of pain
Thalamus- allows person to be aware of painCerebral Cortex- judges intensity of pain, locates source, and motor responses to painLimbic System - produces emotional response to painNatural Pain Inhibiting Substances:Serotonin and Endorphins
Special Senses
localized receptors (taste, smell, vision, hearing, and equilibrium)
Taste
Chemoreceptors are located in taste buds on projections called papillae To activate a taste cell, a chemical must be dissolved in a liquid (saliva)Once receptors are stimulated, impulses travel through cranial nerves VII, IX, & X → medulla oblongata → thalamus → gustatory cortex of cerebrum in the parietal lobes
Taste cells
receptors for taste
umami
Taste receptor formeat/amino acids
Smell
Olfactory organs and chemoreceptor cells are located in upper portion of nasal cavity Cilia on ends of receptors are exposed to airborne particles - "odorant molecules" stimulate these receptorsNerve impulses travel through olfactory bulb → olfactory nerves → limbic system (memory & emotions) and olfactory cortex deep w/in the temporal lobes
Hearing
The ear is the organ of hearing External ear, Middle Ear, Inner ear
External ear
Auricle/pinna, External auditory canal, Tympanic membrane (eardrum)
Auricle/pinna
traps sound waves
External auditory canal
transport sound waves
Tympanic membrane (eardrum)
Sound waves cause it to vibrate
Middle ear
transmit vibrations to inner ear
Inner ear
complex system of chambers & tubes called a labyrinth Semicircular canals. vestibule, cochlea
Semicircular canals and vestibule
functions in equilibrium
Cochlea
major structure for hearingvibrations cause hairs to change shape, stimulating receptor cellschanges sound waves into nerve impulses
Loudness
loud sounds lots of movt of inner ear structures increased rate of nerve signals generated by hair cells and # of hair cells stimulated auditory cortex interprets this as a loud sound measured in decibels (dB)
Static equilibrium
detects position of head, maintains posture/ stability when head and body are still Movt of head forward, backward, side/side causes receptor hair cells to be bent and activated in the vestibulegenerates nerve impulse → travels along vestibular nerve → brain
Dynamic equilibrium
detects motion when the head is moves suddenly rapid turns of head or body → bends hair cells → generates nerve impulse → travels along vestibular nerve → brain
What causes motion sickness?
Receptors in eye says we are still, while the skin senses vibrations and says we are moving. These counteract with each other and make us feel sick
Outer layer of eye
Sclera, Cornea
Sclera
tough, opaque white of the eyeprotectionattachment site for muscles & optic nerve
Cornea
clear anterior portion of scleraHelps focus entering rays of light
Middle layer of eye
choroid coat, ciliary bodies, iris, lens
choroid coat
provides nourishment for surrounding tissues, has blood supplypigments absorb extra light to keep the inside of the eye dark
ciliary bodies
contains muscles that attach to suspensory ligaments
suspensory ligaments
pull on lens to change its shape
Iris
muscle fibers & CT in the anterior part of choroidpigmented, colored part of eyecontrols light intensity by constricting & dilating pupil
pupil
opening in center of iris through which light passes
Lens
transparent, biconvex, elastic largely composed of lens fiberschanges shape to focus on object (accommodation)
Inner layer of eye
retina
retina
(back of eyeball)contains photoreceptors (receptor cells for visionRods and cones
Rods
for black and white vision, sensitive to light and provides vision in dim light, provides "general vision
Cones
for color vision, provides shaper vision, but less sensitive in dim light
Anterior cavity
Space between cornea and lensFilled with aqueous humor
aqueous humor
liquid that maintains the shape of the cornea and regulates internal pressure within the eye
Posterior cavity
Located behind the lensFilled with vitreous humor
vitreous humor
gel-like fluid that presses retina against eye wall
Physiology of vision
Light → cornea → aqueous humor → lens → vitreous humor → photoreceptors in retina → optic nerve → chiasma → thalamus→ visual cortex in occipital lobe of cerebrum