radi 660 gateway 6: neuro

functions of nervous system

maintains homeostasis, sensory monitoring of external and internal environment; sensory, integrative, motor (effectors); sense changes inside and outside the body, interpret these changes, respond to the interpretation (muscle contractions, hormone secretion or other chemicals into the bloodstream)

the efferent division (motor) is…

somatic and autonomic (voluntary and involuntary); AWAY from the CNS

the afferent division (sensory) is…

somatic/visceral, TO the CNS

what are interneurons?

association neurons

describe somatic efferent NS

motor impulses sent to skeletal muscle under conscious control

describe autonomic efferent NS

visceral (internal organs); involuntary; sympathetic and parasympathetic; motor impulses are sent to cardiac and smooth muscle and glandular epithelium

differentiate between glia and neurons

glia do NOT send impulses, support neurons, they make up 90% of the NS and retain capacity for cell division which is good bcus you can get more if damaged but bad bcus risk of dysplasia or anaplasia (most tumors are glial in nature); neurons make up 10% of the NS and DO send impulses

name the 5 types of glial cells

astrocytes, microglia, ependymal cells, oligodendrocytes, schwann cells

axons have _ at the very end

synaptic bulbs

many axons are covered with _ but not all of them

myelin

unmyelinated segments are called _

“nodes of ranvier”

_ make myelin for the CNS

oligodendrocytes

_ make myelin for the PNS

schwann cells

cytoplasm, nucleus, and outer cell membranes cover axons as well as _

nodes of Ranvier

what is neurolemma

track of long axons, important in regeneration of peripheral nerves

largest and most numerous glial cell, found only in the CNS

astrocytes

security cell; forms blood brain barrier - oxygen/carbon dioxide, water, alcohol (change in neuro status), glucose diffuse easily

astrocytes

what are the cons of the blood brain barrier?

if the brain gets infected or there’s a tumor, it’s hard to get meds thru the barrier because they’re seen as toxins

astrocytoma

common brain tumors because astrocytes are the most numerous

clean up crew; small, usually in the CNS; carry on phagocytosis, destroys microorganisms and debris

microglia

help cushion NS with CSF; line fluid-filled cavities in the brain and spinal cord and produce CSF, have cilia that help the fluid circulate

ependymal cells

smaller than astrocytes and fewer processes; hold nerve fibers together, produce myelin sheath in the CNS

oligodendrocytes

found only in the PNS; support nerve fibers, form myelin sheath by layering schwann cells, helps form nodes of Ranvier and form neurolemma

schwann cells

what are the 5 components of a reflex arc?

receptor, sensory neuron, interneuron, motor neuron, effector

explain a simple reflex arc

stimulus triggers receptor to send sensory signal via afferent neuron to the CNS; signal goes to interneuron in the brain/CNS; CNS sends motor signal via efferent neuron to the effector (skeletal muscle) which then produces a response/action

automatic, involuntary, maintains homeostasis (HR, BP, respirations), coughing, sneezing, reactions to pain (ex: withdrawal reflex)

simple reflex arc

what are the 4 nerve plexus?

cervical, brachial, lumbar, sacral

what is required for a nerve impulse

nerves respond to stimulus, need to be stimulated (excitability) enough to reach threshold, conductivity transmits impulses

explain the steps of an action potential

stimulus triggers stimulus-gated sodium channels to open and allow inward sodium diffusion, causing membrane to depolarize; as threshold potential is reached, voltage-gated sodium channels open; as more sodium enters the cell, the membrane depolarizes even further and the magnitude of the action potential peaks at +30 mV when voltage-gated sodium channels close; repolarization begins when voltage-gated potassium channels open, allowing outward diffusion of potassium; after a brief period of hyperpolarization (where an AP cannot be fired), resting potential is restored by the sodium-potassium pump and the return of ion channels to their resting state

what is the “all or none” principle of action potential

they require a stimulus to reach threshold otherwise they don’t fire, they either fire or they don’t, there is no partial action potential

what is saltatory conduction?

in myelinated axons, action potentials can be propagated from node of Ranvier to node of Ranvier

mature neurons are incapable of cell division so damage is permanent; however, cells in the PERIPHERY ONLY can be repaired IF…

damage is not extensive, cell body and neurolemma are intact, scarring has not occurred

describe the nerve repair process

injury occurs, axon degenerates and the myelin sheath, macrophages remove the debris, neurolemma forms a tunnel from the injury to the effector, schwann cells grow in the tunnel, axon sprouts appear, need to find and reach the tunnel, then the growth is accelerated to the effector

why can only PNS neurons repair?

there are no astrocytes in the periphery, only in the central NS; astrocytes can form glial scars in the CNS that inhibit axon regrowth, but the PNS uses Schwann cells which promote neuron regeneration

the brain and spinal cord are continuous at the _

foramen magnum

list the meninges from OUTER/EXTERNAL to INNER/INTERNAL layers

dura, arachnoid, pia

composed of gray matter and ¾ of the cells of the entire nervous system; also in basal ganglia

cerebral cortex

bulk of cerebral hemisphere, myelinated nerve fibers, communication pathways in the cerebrum

white matter

the brain has cerebral hemispheres that are nearly _ in structure but NOT in function

symmetrical

most people (90%) are left hemisphere dominant for _

language and math; you don’t know this until damage occurs

the right hemisphere of the brain is involved in:

motor skills, intuition, art, spatial conceptualization, creativity

Sensory relay station to cortex

Thalamus

Integration and regulation of conscious motor control like posture, walking, and repetitive movements

Basal ganglia

Cardiac center, vasomotor center, respiratory center

medulla oblongata

Hearing, smell, memory

hippocampus

Arousal and wakefulness

RAS reticular activating center

Reflexes, consciousness, motor control, visual and auditory function

Midbrain

Comprehension of speech

Wernicke’s area

Homeostasis, regulates visceral activities, link between CNS and endocrine system; affects and regulates blood pressure, heart rate, hunger, thirst, sexual arousal, and circadian rhythm

hypothalamus

Intellectual function and personality

frontal lobe

Respiratory regulation centers

pons

vision

Primary visual cortex

memory and emotions

limbic system

Motor speech (expression)

Broca’s area

Controls learned motor skills that involve skeletal muscles, either simultaneously or sequentially

Frontal lobe premotor cortex

receives sensory input from receptors in the skin and skeletal muscles

primary sensory cortex (somatosensory cortex)

integrates and analyzes input received by the primary sensory cortex

somatosensory association area

initiates efferent action potentials that control voluntary movements

primary motor cortex (somatomotor cortex)

controls learned motor skills that involve skeletal muscles, either simultaneously or sequentially

premotor cortex

involved with thought, reasoning, intelligence, judgment, planning, and conscience

prefrontal cortex

integrates sensory interpretations from the adjacent association areas to form thoughts, then transmits signals for appropriate responses

gnostic area (general interpretation area)

posture, coordination, parkinson’s disease (don’t make enough dopamine which is an inhibitory neurotransmitter, so these pts have rigidity and tremors)

basal ganglia

grad central station; transfers info; centrally located, nearly surrounded by cerebral hemispheres; contains the thalamus, hypothalamus, and epithalamus

diencephalon

sensory relay station to cortex; 80% of diencephalon

thalamus

homeostasis, regulates visceral activities, link between CNS and endocrine system

hypothalamus

dorsal portion of diencephalon; contains the pineal gland, which affects onset of puberty, rhythmic cycles of the body, and our “biological clock”

epithalamus

scattered, interconnected areas of gray matter in the hemispheres and diencephalon; controls memory and emotions

limbic system

in the limbic system, controls learning and memory

hippocampus

in the limbic system, regulates emotions, especially aggression, gives emotions meaning; abnormal function may make people more prone to violence

amygdala

in the limbic system, affects and regulates BP, HR, hunger, thirst, sexual arousal, and the circadian rhythm sleep/wake cycle

hypothalamus

parts of the brainstem:

midbrain, pons, medulla oblongata

most superior brainstem; controls reflexes, consciousness, motor control, visual and auditory function

midbrain

bulging mid-portion of brainstem; crossing fibers of cerebellum; where four cranial nerves originate; respiratory regulation centers

pons

respiratory regulation center that transmits inhibitory impulses to the inspiratory area to help turn off inspiration area before the lungs become too full of air; impulses shorten the duration of inhalation

pneumotaxic area

respiratory regulation center that actives inspiratory area to deepen breaths/prolong inspiration

apneustic area

extends inferiorly from the pons and is continuous with the spinal cord; contains all sensory and motor nerves connecting spinal cord and brain, most of motor nerves cross over (decussation)

medulla oblongata

cardiac center, vasomotor center, respiratory center

medulla oblongata

has a branching pattern called arbor vitae

cerebellum/cerebellar cortex

coordination, balance, posture; one of first areas affected by alcohol, hence the police field line test

cerebellum

the ventricular system contains:

lateral ventricles, third ventricle, fourth ventricle, choroid plexus (circulates CSF around the brain)

the spinal cord extends from _ to _

foramen magnum; L1

the spinal cord terminates in _

conus medullaris

spinal cord meninges extend from _ to _

conus medullaris; sacrum @ filum terminale

spinal nerves extending below the conus medullaris are called _

cauda equina (horses tail)

stressful or emergency situations, fight or flight, energy-expending; increases BP, HR, breathing, blood flow to skeletal muscle, decreases GI activity

sympathetic autonomic NS

rest and digest, aids with digestion, relaxes sphincters, increased digestive enzymes and peristalsis at rest, decreases HR

parasympathetic autonomic NS

signs related to the specific area of the brain or spinal cord in which lesion is located; example: paresis or paralysis of the right arm may be result from damage to a section of the left frontal lobe; also could be due to expanding lesions like a growing tumor or hemorrhage; additional impairment is noted as adjacent areas become involved

local (focal) effects of neurologic dysfunction

loss of logical thinking ability, analytical skills, other intellectual abilities, communication skills

damage to left hemisphere

impairs appreciation of music and art, causes behavioral problems, spatial orientation and recognition of relationships may be deficient, self-care deficits are common

damage to right hemisphere

how is LOC affected early with acute brain disorders?

decreased level of consciousness or responsiveness

levels of reduced consciousness may be…

confusion and disorientation, memory loss, unresponsiveness to verbal stimuli, difficulty in arousal, loss of consciousness or coma

damage to upper motor neurons causes…

interference with voluntary movements, weakness or paralysis on the contralateral side of the body

damage to lower motor neurons causes…

weakness or paralysis on the same side of the body, at and below the level of spinal cord damage

decorticate and decerebrate posturing occurs when there is…

severe brain damage

inability to comprehend or express language; if receptive —> damage to wernicke’s area; if expressive —> damage to broca’s area; if mixed/global —> damage to both areas or to the fibers and tracts between them

aphasia

motor dysfunction affecting muscles used in speech

dysarthria

damage to broca’s area/left frontal lobe; cannot speak or write fluently or appropriately

expressive (motor) aphasia

damage to wernicke’s area/left temporal lobe, prefrontal; unable to understand written or spoken language

receptive (sensory) aphasia

damage to broca’s and wernicke’s areas and connecting fibers; cannot express self or comprehend others’ language

global aphasia

impaired ability to speak or write fluently or appropriately; occurs when broca’s area in dominant frontal lobe is damaged

expressive or motor aphasia