4. Neuron Anatomy and Physiology

basic anatomic functional unit in the CNS

neuron (nerve cell)

number of neurons in CNS

86 billion

multipolar shape

one axon with many dendrites

Golgi type 1

long and large diameter axons

Golgi type 2

shorter, narrower axons

Motor neuron function

efferent

brain to body

Sensory neuron function

afferent

body to brain

purpose of neurons

regulate sensorimotor and higher functions

Glial cells purpose

protection of nerve cells and tissue repair

nucleus

site of DNA

in cell body

dendrites

afferent fibers

transmission of information to cell body from other cells

axons

efferent

transmission of information away to other neurons or target organs

communication within cells

electrical signals

action potentials

communication between cells

chemical

via neurotransmitters

membrane potential

the difference in electrical potential (charge) across a cell membrane

resting potential

potential of unstimulated neuron

action potential definition

movement of ions across the cell membrane to transmit a signal

ion

charged partical

channel proteins

proteins in the cell membrane that allow only certain ions to pass through under certain conditions

protein pumps

mechanisms that actively move ions into/out of the cell

require ATP energy

sodium potassium pump purpose

mechanism that maintains resting potential

polarization

positive electrical charge on one surface and negative on the other surface

hyperpolarization

inside the cell becomes MORE negative; less likely to generate signal

depolarization

inside the cell becomes less negative and more likely to generate an action potential

gradient

different concentrations across the cell membrane

electrical gradient

more negative ions inside the cell and more positive ions outside the cell

ion concentration gradient

banana rolled in salt

Na+ outside K+ inside

basic ion channel

basic channels always open, allow free movement for select ions

ligand-gated channels

open when neurotransmitters bind to them

mechanically gated channels

open in response to mechanical displacement

voltage gated channels

open in response to voltage changes

ligand-gated channels location

post-synaptic membranes

mechanically gated channels location

sensory systems

voltage-gated channels location

axon and axon terminal

excitatory signals cause what

depolarization

inhibitory signals cause what during action potential

hyperpolarization

summation of ESPSs and IPSPs location

soma

summation of ESPSs and IPSPs equals

determination of whether action potential is created

action potential steps

1. ESPSs summate near the axon hillock, enough Na+ enters to reach threshold
2. Rapid opening of many voltage-gated Na+ channels in axon, created depolarization by Na+ rushing in
3. repolarization begins, Na+ channels close and inactivate
4. K+ channels open, K+ moves out of the cell, repolarization & refractory period
5. cell becomes more negative-hyperpolarization
6. Na+/K+ pump activates to restore resting potential using ATP

how does action potential move

proximal to distal down axon to terminal buton

where does exchange of ions occur

nodes of ranvier

ESPSs

excitatory signal

ISPSs

inhibitory signal

synapse definition

site of communication between nerve cells

presynaptic neuron

axon ends in terminal buttons

neurotransmitters stored in and released from vesicles

synaptic cleft/gap

space between neurons

post synaptic neuron

contains receptor proteins that bind with neurotransmitters to either excite or inhibit

synaptic communication occurs

through neurotransmitters released from terminal butons by action potential

synaptic transmission steps

1. neurotransmitters released into synaptic gap
2. bind to neurotransmitter-specific receptors
3. neurotransmitter releases from receptor
4. neurotransmitter recycled (reuptake) or destroyed via enzymes

resting electric potential

\-70 mV inside cell

membrane potential

uneven distribution of Na+ K+ Cl-

more intense stimuli

more signals

source of signals

different neurons respond to different signals

divergent signal

widespread

convergent signal

focused

reverberating signal

continuous

serial signal

single chain

parallel signal

sent through multiple tracts

MS cause

antibodies randomly attack myelin

affecting nerve conduction speed

30-40 yr old onset

multiple sclerosis early symptoms

nerve conduction speed affected

based on lesion location

vision loss/double vision

impaired balance

vertigo

numbness

weakness of limbs

MS late symptoms

nystagmus

scanning speech

intention tremor

cognitive impairment

dysphagia

MS treatment

symptomatic treatment

corticosteroid drugs

beta-interferon injections

MS SLP role

combo of direct treatment to improve impairments, compensatory strategies, education

keep muscles strong

Guillain Barre Syndrome symptoms

progressive sensorimotor deficits that spread to upper limbs and face

progress up to 4 weeks

can be life-threatening with respiratory or bulbar palsy

Guillain Barre SLP role

swallow evals

muscle strengthening

difference between MS and Guillain Barre

MS=autoimmune disorder of CNS

GB=autoimmune disorder of PNS

Glutamate purpose

main excitatory CNS nt

involved in learning, memory, thinking

Glutamate problems

excitotoxicity-after stroke/brain injury there can be too much glutamate which damages CNS neurons

seizures

NT disorder causes

supply issues

altered reuptake

blocked post-synaptic receptors

seizure treatment

pharmacologic GABA transmitters to inhibit firing

occasionally surgical

Stroke treatment

pharmacologic

rest

SLP role with seizure/stroke

cognitive impairments

wait before initiating intensive tx

GABA purpose

widespread inhibitory CNS nt

used to treat epilepsy, anxiety, insomnia

GABA problems

Huntington’s Chorea

Huntington’s Disease symptoms

speech, swallowing, cognitive communication impairments

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Huntington’s disease SLP role

compensation and education of pt and caregivers

dopamine functions

motivation

reward anticipation

addiction

movement

insufficient dopamine production

Parkinson’s disease

Parkinson’s symptoms

decreased ability to regulate movement and emotions

cognitive impairments

dysarthria

dysphagia

SLP and PD

LSVT loud/speak out for hypokinetic dysarthria

recalibrating speech

assist with swallowing

norepinephrine function

fight or flight

sleep

attention

insufficient supply of norepinephrine problems

depression and anxiety

drugs that inhibit reuptake of norepinephrine/serotonin (Prozac) treats

depression, anxiety, chronic pain

serotonin function

arousal

sleep

pain control

low serotonin effects

depression

acetylcholine function

regulates muscle activity

sleep/wakefulness

cause of myasthenia gravis (MG)

antibodies block receptors at neuromuscular junctions sp acetylcholine can’t bind

MG symptoms

muscle fatigue (weakness with exertion, improvement with rest)

ptosis (drooping eyelids)

diplopia (double vision)

gradual onset

most affects constantly used muscles (eye, respiratory)

altered facial expression, choking, hypernasality, dropped jaw

MG treatment

pharmacologic

SLP

SLP role MG

speech and swallowing assessment

education

compensatory strategies-safe foods, smaller more frequent meals

NO DIRECT TREATMENT

astrocytes location

CNS (gray and white matter)

oligodendrocytes location

CNS

astrocytes function

regulates transmission of substances across blood vessels

form scars around dead brain tissue

oligodendrocytes function

form myelin sheaths around axons in CNS

microglia location

CNS

microglia function

travel to site of lesion and engulf debris

ependymal cells location

ventricular cavity

ependymal cells function

lining around ventricular surface

schwann cells location

PNS

schwann cells function

form myelin sheath around axons in PNS

make up fibrous connective tissue around fibers in PNS