Action Potential
occurs when a stimulus of sufficient strength depolarizes the cell
Depolarization
when the charges of the inside and the outside switch
Repolarization
Return to resting membrane potential
- K+ leaves the cell rapidly
- Na+ channels close
All-or-none law
once a nerve impulse is initiated, it will travel the length of the neuron
Synapse
a small gap between presynaptic neuron and postsynaptic neuron
Neurotransmitter
- a chemical released from presynaptic membrane in response to the depolarization of a neuron
- binds to receptor on postsynaptic membrane
- causes depolarization of postsynaptic membrane
Excitatory postsynaotic potentials (EPSP)
- causes depolarization in postsynaptic neuron
Temporal summation
summing several EPSPs from one presynaptic neuron
Spatial summation
summing from several different presynaptic neurons
Inhibitory postsynaptic potentials (IPSP)
causes hyperpolarization
Gamma - aminobutyric acis (GABA)
opens cl channels and cause hyperpolarizatioin
Functions of the Nervous System
- control of the internal environment
- voluntary control of movment
- programming spinal cord reflexes
- assimilation of experiences necessary for memory and learning
Organization of the nervous system
- central nervous system (CNS)
- peripheral nervous system (PNS)
Central Nervous System (CNS)
- brain and spinal cord
Peripheral nervous system
- neurons outside the CNS
-Sensory division (afferent fiber transmit impulses from receptors to CNS)
- Motor division (efferent fibers transmit impulses from CNS to effector organs)
Dendrites
conduct impulses toward the cell body
Axon
carries electrical impulses away from cell body toward another neuron or effector organ
Axon terminal
at the end of axon containing neurotransmitters
Axon hillock
generates action potential
Myelin Sheath
- formed by schwann cells
- insulating envelope surrounding the core of an axon and facilitating the transmission of nerve impulses
Neurons are an _______ tissue
excitable
Neurons have irritablilty. What does this mean?
the ability to respond to a stimulus and convert it to a neural impulse
Neurons have conductivity. What does this mean?
transmission of the impulse along the axon
Inside of the cell there is a ________ charge at rest.
negative
Resting membrane potential is determined by:
- permeability of plasma membrane to ions
- difference in ion concentrations across membrane
resting membrane potential is maintained by:
sodium - potasium pump
- potassium tends to diffuse out of cell
-NA+/K+ pump moves 2 K+ in and 3 Na+ out
Which ions are high inside the cell?
Which ions are high outside the cell?
Only potassium (K+) is high inside the cell
Cl-, CA+, and NA+ are high outside the cell
Nerve cells are called __________ and are divided anatomically into 3 parts: _______, ________, and ______
neurons; cell body, dendrites, and the axon
Axons are generally covered by _______ cells, w/ gaps between thses cells called ______________.
Schwann; nodes of Ranvier
At rest, neurons are _____ charged in the interior with respect to the electrical charge outside the cell. This difference in electrical charge is called the __________________.
negatively; resting membrane potential
A neuron "fires" when
a stimulus changes the permeability of the membrane, allowing sodium to enter, which depolarizes the cell
Repolarization occurs immediately following depolarization due to
an increase in membrane permeability to potassium and a decreased permeability to sodium
Neurons communicate with other neurons at junctions called _____.
synapses
Synaptic transmission occurs when
sufficient amounts of a specific neurotransmitter are released from the presynaptic neuron. Upon release, the neurotransmitter binds to a receptor on the postsynaptic membrane
neurotransmitters can be
excitatory or inhibitory
An excitatory neurotransmitter
increases neural permeability to sodium and results in excitatory postsynaptic potentials (EPSPs)
An inhibitory neurotransmitter
cause the neuron to become more negative (hyperoplarized). the hyperpolarization of the membrane is called an inhibitory postsynaptic potental (IPSP)
Proprioceptors
- receptors that provide CNS w/ information about body position
- located in muscles, tendons, joints, and the inner ear
- detects the motion or position of the body or a limb
Free Nerve Endings
- in the skin
- sensitive to touch and pressure
- initially strong stimulated, the adapts
Golgi-type receptors
- found in ligaments and around joints
- similar to free nerve endings
- since rotation/movement of a joint
Pacinian corpuscles
- in tissues around joints
- detect rate of joint rotation
Muscle proprioceptors
- provide sensory feedback to nervous system (tension development by muscle & account of muscle length)
- 2 types: muscle spindle and golgi tendon organ
Another name for Muscle Spindle
the length detector
Function of the muscle spindle:
- provide fiber length information to CNS
- help in fine tuning of muscle strength
- responsible for stretch reflex
- length detector in muscle
Which part of the body has the most muscle spindles?
the Hand
Muscle spindles consist of
- intrafusal fibers
- gamma motor neurons
Inrafusal fibers
run parallel to normal muscle fibers (extreafusal fibers)
Gamma motor neurons
stimulate intrafusal fibers to contract with extrafusal fiber (by alpha motor neuron)
Stretch reflex
stretch on muscle causes reflex contraction
Golgi tendon organ (GTO) location
in the tendons
function of the golgi tendon organ (GTO)
- monitors tension developed in muscle
- prevents muscle damage during excessive force generation
- sends feedback to reduce the force of muscle contration
nickname for the golgi tendon organ (GTO)
safety device
stimulation of the golgi tendon organ results in what?
in reflex relaxation of muscle
(inhibitory neurons send IPSPs to muscle fibers)
When you train the "safety device" what happens?
muscle strength increases; sensory threshold increases; muscle contraction increases
(golgi tendon organ is reset at a higher level due to increased muscle fiber strength)
When testing your patella tendon, the swing of your lower leg is due to what?
stretch reflex by contraction of the muscle spindle
What happens when someone stretches ("pull") their tendon?
the person pushed themselves to far; the cortex is extremely high (very excitable)
excitation from the brain and spinal cord over rides the golgi tendon organ or the person overtrained their muscle and it became weak
Muscle chemoreceptors
- sensitive to changes in the chemical environment surrounding the muscle
- provide CNS about metabolic rate of muscular activity
muscle chemoreceptors are important in regulation of:
cardiovascular and pulmonary responses
What are reflexes?
rapid unconscious means of reacting to stimuli
Reflexs are integrated where
only to the spinal cord
order of events for reflexes:
- sensory nerve sends impulse to spinal column
- interneurons activate motor neurons
- motor neurons control movement of muscles
Reciprocal inhibition
excitatory and inhibitory activities occur simultaneously
- EPSPs to muscles to withdraw from stimulus
-IPSPs to antagonistic (opposes) muscles
Crossed-extensor reflex
...
After you reflexes are triggered what is immediately triggered
alpha motor neurons
Where are proprioceptors located
in joint capsules. ligaments, and muscles
somatic motor neurons
- alpha motor neurons innervate skeletal muscles
what is a motor unit
motor neuron and all the muscle fibers it innervates
innervation ratio
number of muscle fibers per motor neuron
1 motor neuron and its axon terminal can innervate:
many muscle fibers
When a motor neuron is needed for precision type work it is _______, but they are naturally ________.
big; small
Vestibular apparatus: location
in the inner ear
vestibular apparatus: function
- responsible for maintaining general equilibrium and balance
- sensitive to changes in linear and angular acceleration
- controls head and eye movement during exercise
the brain stem is responsible for
- connecting brain & spinal cord
- maintaining postural tone
- eye movement & muscle tone
- cardiorespiratory control (contain major autonomic regulatory center, respiratory and cardiovascular system
brain stem includes:
- medulla
- midbrain
- pons
- medulla oblongata
Cerebrum contains what?
- cerebral cortex
- motor cortex
cerebral cortex
- part of the cerebrum
- organization of complex movement
- storage of learned experiences
- reception of sensory information
motor cortex
- part of the cerebrum
- motor control and voluntary movement
cerebellum: function
- coordinates and monitors complex movement (incorporates feedback from proprioceptors)
- may initiate fast, ballistic movements
cerebellum has connections to:
- motor cortex
- brain stem
- spinal cord
cerebellum: location
back bottom portion of the head
3 subdivisions of the brain
- brain stem
- cerebrum
- cerebellum
spinal cord reglexes
- withdraw reflex
- stretch reflex
- inversed myotatic reflex (GTO)
- some reflexes can be trained
Spinal tuning
-voluntary movement translated into appropriate muscle action
Subcortical and cortical motivation areas
send a "rough draft" of the movement
Cerebellum and basal ganglia
- convert "rough draft" into movement plan
- Cerebellum: fast movements
- Basal ganglia: slow, deliberate movements
Motor cortex through thalamus
- forwards message sent down spinal neurons for "spinal tuning" and onto muscles
- feedback from muscle receptors and proprioceptors allows fine tuning of motor program
autonomic nervous system: general functions
- homeostasis
- control visceral (internal organs) function
- support somatic reactions
what are the parts of the autonomic nervous system?
- sympathetic and parasympathetic system
Sympathetic system
- part of the autonomic nervous system
- in the thoracic and lumbar spinal cord
- how you deal with stressful environments
- release norepinephrine
parasympathetic system
- part of the autonomic nervous system
- in the brain stem and sacral spinal cord
- reciprocal of the sympathetic system
- release acetylcholine
- inhibits what the sympathetic stimulates
the higher the intensity you exercise, the ______ the sympathetic system will perform
higher
When the sympathetic system is stimulated your GI tract and salivary gland ____________
decreases
When the sympathetic system is stimulated your GI tract and salivary gland ____________
increase