Nervous system

What does nervous system consist of

brain, spinal cord, nerves

What does nervous system do

Receives stimuli, processes info, decides what to do, sends impulses to cells to tell them how to respond

three roles of the nervous system

sensing - receives stimuli

integrating - processing info and figuring out appropriate response

responding - issues commands to respond to stimuli

two main divisions of nervous system

central nervous system - brain and spinal cord

peripheral nervous system - network of nerves throughout body

what are the divisions of the peripheral nervous system

sensory division - afferent

motor division - efferent

what are the divisions of the sensory division in PNS

somatic sensory - carries signals from skin, bones, joints, muscles

visceral sensory - carries signals from organs

what are the divisions of the motor division in PNS

somatic motor - voluntary motor movements

autonomic motor - “automatic” motor movements

what are the divisions of autonomic motor in PNS

sympathetic division - “fight or flight” automatic responses

parasympathetic division - “rest and digest” automatic responses

two types of cells that can be found in nervous system (both CNS and PNS)

neuron - does the transmitting/communicating

neuroglia/glial cells - supports and protects neurons

what are the types of glial cells in CNS

oligodendrocytes - forms myelin sheath

ependymal cells - lines spinal cord and brain cavities, secretes cerebrospinal fluid, has cilia

microglia - performs phagocytosis (“eating” of molecules, active transport)

astrocytes - present throughout brain tissue, nourishes neurons, forms blood brain barrier, attaches neurons to blood vessels, etc most abundant and versatile

what are the glial cells in PNS

schwann cells - forms myelin sheath

what does the blood brain barrier do

allows small molecules to diffuse to brain and blocks larger molecules. protection but can also make it hard for some meds to get to brain

3 types of neurons

sensory/afferent neurons - detects stimuli

interneurons - connects sensory pathways with motor pathways. only found in CNS

motor/efferent neurons - sends message from brain to muscle or gland cells

name and describe the different components of a neuron

soma/cell body - control center

dendrites - receiver

axon - sender

myelin sheath - protective cover over axon. speeds up transmission. formed by oligodendocytes and schwann cells

nodes of ranvier - gaps in myelin sheath

synaptic knob - end of the axon. inside are vesicles containing a neurotransmitter

describe the myelin sheath of a neuron in PNS

schwann cells are wrapped around the axon forming the outer layer of the sheath (neurilemma)

what is neurilemma

outer layer of a myelin sheath of a neuron in the PNS. contains schwann cells. essential for nerve regeneration

describe the myelin sheath of a neuron in CNS

oligodendrocyte nucleus is separate from the sheath and forms the sheath for multiple axons at a time

what is myelin made of

lipids - fat

when is myelination complete

late adolescence. thats why its important for children to have a diet rich in dietary fat

impulse conduction inside neurons steps

1) resting potential - inside of cell has negative charge and has K (potassium) ions, outside has positive charge and has Na (sodium) ions

2) depolarization - stimulus reaches threshold high enough to depolarize neuron. voltage gated Na channels open on neuron cell membrane and allows Na to enter

3) action potential - more voltage gated Na channels open. Na continues to enter going down the axon

4) repolarization - Na stops entering. voltage gated K channels open. K leaves cell. Charge inside turns negative, charge outside turns positive

5) refractory period - potassium sodium pumps restore Na and K to righful places. cell ready to receive another impulse

what is membrane potential

when ions with opposite charges are separated by a membrane

what is polarization

when membrane has excess of positive ions on one side and excess of negative ions on other side

how many Na and K does the porassium sodium pumps move during the refractory period of impulse conduction

3 Na, 2 K

name for the electrical signal that travels along the axon

action potential or impulse conduction

what is the gap where nerve impulses travel from one neuron to another neuron or tissue

synaptic gap/cleft

the impulse conduction in the synaptic gap is _____, while the impulse conduction in the neuron is _____

chemical, electric

steps of synapse

1) action potential reaches synaptic knob and opens up voltage gated Ca2+ (calcium) channels. Ca2+ enters

2) Ca2+ causes vesicles in the synaptic knobs containing a neurotransmitters to perform exocytosis

3) neurotransmitter binds to a suitable receptor on the postsynaptic neuron’s dendrite

4) the specific neurotransmitter determines if impulse is to continue or be stopped. If excitatory, Na channels open. If inhibitory, K channels open

what is the spinal cord referenced as

an information passageway

how many pairs of spinal nerves are there that branch out from the spinal cord

31 pairs

where does the spinal cord start and stop

start at base of brain until the L1 vertebra

cauda equina

bundle of nerve roots extending from bottom end of spinal cord

what do nerves in the cervical region of the spinal cord innervate

head, neck, shoulders, chest, arms, diaphragm, hands

what do nerves in the thoracic region of the spinal cord innervate

ribs, abdominal muscles, back muscles

what do nerves in the lumbar region of the spinal cord innervate

lower abdominal wall, sides and front of thighs

what do nerves in the sacral region of the spinal cord innervate

back of thigh, buttocks, anal and genital regions, and leg below knee

true or false: spinal cord is shorter than vertebral column

false, spinal cord is shorter than vertebral column

what is gray matter

bundles of neuron cell bodies. cell bodies do not have myelin covering it which is why gray matter is gray

what is white matter

bundles of neuron axons. these axons are covered by myelin sheath which is what gives it its white color

whats another word for white matter

tracts

epidural space

space between outer covering of spinal cord and vertebrae. fatty and has blood vessels. protection

central canal

small canal in the middle of spinal cord that contains cerebrospinal fluid

do the posterior/dorsal horns receive or send

receives sensory info

do the anterior/ventral horns receive or send

sends motor info

what does the posterior/dorsal nerve root do

carries sensory info into the posterior/dorsal horn of the spinal cord

what does the anterior/ventral nerve root do

carries motor info out of the anterior/ventral horn of the spinal cord

ganglion of the posterior/dorsal nerve root

knot like structure made of cell bodies

mixed nerve

a nerve that transmits impulses in two directions

what are the meninges (and spaces) layers from innermost to outermost in the spinal cord

pia mater

subarachnoid space - filled with cerebrospinal fluid

arachnoid mater

dura mater

what are spinal tracts and what is their function

bundles of axons in the white matter that serves as routes of communication to/from the brain

what are the ascending tracts

dorsal column - relays deep pressure and vibration sensations. also relays sensations for proprioception (body spatial awareness)

spinocerebellar - responsible for proprioception

spinothalamic - relays temperature, pressure, pain, touch sensations

dorsal column spinal tract

relays deep pressure and vibration sensations. relays sensations needed for proprioception (body spatial awareness) up to brain

spinocerebellar spinal tract

relays info needed for proprioception up to brain

spinothalamic spinal tract

relays temperature, pressure, pain, touch sensations up to brain

what are the descending tracts

corticospinal - responsible for fine movements of hands, fingers, feet, toes on opposite side of body

extrapyramidal - responsible for balance and muscle tone

corticospinal spinal tracts

carries impulses for fine movements in hands, fingers, feet, toes on opposite side of body from the brain

extrapyramidal spinal tracts

carries impulses for balance and muscle tone from the brain

decussation

when spinal cord tracts cross at the brain stem

ascending tracts bring ______, while descending tracts bring _______

sensory info to the brain, motor info from the brain

what are tracts in the PNS called

spinal nerves

fascicles

bundles of nerve fibers in spinal nerves

what are the 31 pairs of spinal nerves that connect to the spinal cord

8 cranial nerves

12 thoracic nerves

5 lumbar nerves

5 sacral nerves

1 coccygeal nerve

plexus

network of subdivided spinal nerves with specific areas they innervate

what are the four major plexus

cervical - contains nerves that innervate muscles and skin of neck, tops of shoulders, and part of head

brachial - contains nerves that innervate muscles in lower part of shoulder and arm

lumbar - contains nerves that innervate muscles in the thigh and leg

sacral - contains muscles that innervate muscles in the posterior side of the lower body (below waist)

important nerve to remember in cervical plexus

phrenic nerve - controls diaphragm

important nerves to remember in brachial plexus

axillary nerve

radial nerve

ulnar nerve

median nerve

important nerve to remember in lumbar plexus

femoral nerve

important nerve to remember in sacral plexus

sciatic nerve - longest nerve in body

what areas does the cervical plexus innervate

skin and muscle of head, tops of shoulders, part of the head

what areas does the brachial plexus innervate

lower part of shoulder and arm

what areas does the lumbar plexus innervate

thigh and leg

what areas does the sacral plexus innervate

posterior side of lower extremity (from waist down)

dermatomes

areas of the skin innervated by certain spinal nerves at specific levels of the spine

why are dermatomes assessed by clinicians

helps assess location and severity of spinal cord injury or abnormality

myotome

groups of muscles innervated by certain spinal nerves at specific levels of the spine

how do spinal cord injuries occur

traumatic impact causes vertebra to fracture, spreading bone fragments that damage the spinal cord. pressure from the event also causes compression to vertebrae and spinal cord within it

why is spinal cord injury at C4 dangerous

the phrenic nerve exits the spinal cord in that area, causing respiratory failure

reflex arc

the travelling of nerve impulses that bypasses the brain

explain the steps to the somatic reflex arc

1) receptors in skin/muscle/tendon detect sensation

2) sensory info travels through PNS by way of afferent sensory neurons and enter the posterior/dorsal horn of the gray matter of the spinal cord

3) interneuron inside the gray matter processes sensory info and turns it into motor command

4) efferent motor neurons deliver motor info back to skin/muscle/tendon but exiting the anterior/ventral horn

what does babinski test

tests if there is an issue in the central nervous system

what is a favorable result for the babinski test

toes curl down

what is a result from the babinski test that indicates CNS issues

big toe points up and rest of toes splay out

does an infant experiencing a babinski sign have CNS issues

not necessarily, infants before the age of 12-18 months do not have fully developed nervous systems and may exhibit the babinski sign even though they have no CNS issues

gyri

ridge in the brain. lumpy bumpy

sulci

shallow grooves in brain

fissure

deep grooves in brain

corpus collosum

bundle of nerves that connect the two hemispheres of the brain

longitudinal fissure

deep groove that separates the brain into hemispheres

where is the gray and white matter in the brain

gray matter outside, white matter inside

where is the gray and white matter in the spine

gray matter inside, white matter outside

cerebral cortex

layer of grey matter on the surface of the brain

basal nuclei

gray matter in the brain that exists throughout the white matter

name the meninges (and spaces) found on the brain in order from innermost to outermost

pia mater

subarachnoid space

arachnoid mater

subdural space

dura mater

name the layers of the dura mater in the brain from innermost to outermost

meningeal layer

periosteal layer

dural sinuses

spaces in brain created when dura mater separates. collects blood that has passed through the brain

possible symptoms arising from traumatic brain injury

dizziness, sensitivity to light, fatigue, headache, loss of consciousness, mood disturbances, slurred speech, seizures

ventricles

chambers in the brain that hold cerebrospinal fluid. they attach to one another and eventually connects to the central canal of the spinal cord

purpose of cerebrospinal fluid

provides nourishment to brain (glucose and protein), removes waste, protects, maintains homeostasis

hydrocephalus

condition where a blockage anywhere in CSF route allows ventricles to fill up with CSF causing increased pressure in the head and increased head size in infants.

what does brainstem consist of

midbrain

pons

medulla oblongata