Nervous System

Central Nervous System (CNS)

is in control of the internal environment (with help of the endocrine system) and motor functions

made up of brain and spinal cord

Peripheral Nervous System (PNS)

consists of the neurons outside the CNS

this is in charge of connecting the CNS to the rest of the body

Afferent Fibers

sensory division of the PNS, transmit impulses from the receptors to the CNS

Efferent Fibers

motor division of PNS, transmits impulses from CNS to effector organs

Somatic Nervous System and Autonomic Nervous System

Somatic = skeletal muscles

Autonomic = smooth muscle and cardiac muscle glands

Sympathetic Nervous System

Releases norepinephrine and excites an effector organ; increases during exercises

Parasympathetic Nervous System

Releases actetylcholine (ACh)

Soma

neuron cell body, contains the nucleus

Dendrites

conduct impulses toward the cell body and receives neural information

Axon

nerve fiber that carries electrical impulses away from the cell body and may be covered in

Multiple Sclerosis

Neurological Disease that destroys myelin sheaths of axons, genetic component leads to immune on attack on myelin

Irritability in Neurons

ability to respond to a stimulus and convert it to a neural impulse

Conductivity in Neurons

transmission of the impulse along the axon

Resting Membrane Potential

charge inside cells are negatively charged and usually sit at -5 to -100mv

this is caused by cellular proteins or phosphate groups that are negatively charged and are stuck inside the cell because they cannot cross the cell membrane

Action Potential

rapid changes in membrane potential that occurs when a nerve cell membrane is stimulated

occurs when a stimulus of sufficient strength depolarizes the cell

Depolarization

Na+ channels open and Na+ diffuses into cell so that the inside becomes more positive

Repolarization

return to resting membrane potential immediately following depolarization Na+ channels close and K+ leaves the cell rapidly

All or None Law

once a nerve impulse is initiated, it will travel the entire length of the neuron without losing strength

Synapse

communicate with other neurons at junctions

Neurotransmitter

chemical messenger released from presynaptic membrane

binds to receptor on postsynaptic membrane and causes depolarization

Excitatory Postsynaptic Potentials (EPSP)

causes depolarization

Temporal Summation

Summing several EPSPs from one presynaptic neuron

Spatial Summation

summing from several different presynaptic neurons

Proprioceptors

receptors that provide CNS with information about body positions located in the joints and muscles

kinesthesia

conscious recognition of the position of body parts

Muscle Spindle

Provides information about changes in muscle length

Golgi Tendon Organ

provides information about changes in muscle tension and prevents muscle damage

Proprioceptors During a Bicep Curl

Extension: Muscle Spindles

Flexion: Golgi Tendon Organ

Alpha Motor Neurons

extrafusal muscle fibers, motor related

Gamma Motor Neurons

intrafusal muscle fibers, sensory related

Muscle Spindle Pathway

1) muscle spindles detect stretch of muscle

2) sensory neurons conduct action potentials to the spinal cord

3) sensory neurons synapse with alpha motor neurons

4) stimulation of the alpha motor neurons causes the muscle to contract and resist being stretched

Golgi Tendon Organ Pathway

1) golgi tendon organs detect applied to a tendon

2) sensory neurons conduct action potentials to the spinal cord

3) sensory neurons synapse with inhibitory interneurons that synapse with alpha motor neurons

4) inhibition of the alpha motor neurons causes muscle relaxation, relieving tension applied to the tendon

Muscle Chemoreceptors

sensitive to changes in chemical environment surrounding a muscle and provide CNS with metabolic rate of muscular activity

Cerebrum

outermost layer (cerebral cortex)- organizes complex movements, storage of learned experiences and reception of sensory information

motor cortex- most concerned with voluntary movement and final relay point upon motor control and voluntary movement inputs

Parkinson’s Disease

dopamine (neurotransmitter) levels are decreased

results in: rigidity and trembling of head / extremities, forward tilt of trunk, reduced arm swinging, shuffling gait and short steps

Multiple Sclerosis

neurological disease that destroys myelin sheaths of axons; has a genetic component

results in: progressive loss of nervous system, fatigue, muscle weakness, poor motor control, loss of balance, mental depression

Brainstem

made up of midbrain, medulla, pons

responsible for many metabolic functions and cardiorespiratory control

complex reflexes like control of eye movement/muscle tone, equilibrium, support of the body against gravity, and many special reflexes

Cerebellum

uses feedback from proprioceptors to coordinate and monitor complex movement

has connections to the motor cortex, brain stem, and spinal cord

may initiate fast movements bc of the connection to the motor cortex

Vestibular Apparatus

located in the inner ear, it’s responsible for maintaining general equilibrium and balance while maintaining head position

sensitive to changes in linear and angular acceleration

Somatic Motor Function

carries neural messages from the spinal cord to the skeletal muscles and is responsible for muscle contractions

Motor Unit

single motor neuron and all the muscle fibers it innervates

follows the all or non law and all muscle fibers that a motor neuron innervates are stimulated to contract

Innervation Ratio

the number of muscle fibers innervated by a single motor neuron

# of muscle fiber / motor neuron

Low Innervation Ratio

fine motor control

23/1 in extraocular muscles that regulate eye movement

High Innervation Ratio

gross motor control

1,000/1 or greater in leg muscles

Motor Unit Recruitment

the progressive activation of more and more motor neurons to activate more muscle fibers and increase the strength of a voluntary muscle contraction

they are recruited in size order, smallest motor neurons go first, followed by larger and larger motor neurons

Control of Motor Functions

1) subcortical/cortical motivations areas send “rough draft” to cerebellum or basal ganglia

2) cerebellum (fast movements) and basal ganglia (slow movements) turn it into movement plan

3) message is sent down spinal neurons for spinal tuning and onto muscles

4) feedback from muscle receptors and proprioceptors allows fine tuning of motor program