nervous system Flashcards
the nervous system
2 systems for mainitaing internal coordinations:
- endocrine system (chemical)
- nervous system (electrical AND chemical)
central nervous sytem (CNS)
brain and spinal cord
peripheral nervous system (PNS)
nerves and ganglia
classes of nerouns
- sensory (afferent): detect stimuli
- interneurons (association neurons): receieve signals from other neruosn and process, store, retrieve, and make descisions about the signal (integration)
- motor (efferent): respond to stimuli
neuronal variety
named for the numbers of axons and dendrites at the soma
- multipolar: many dendrites, one axon
- bipolar: one dendrites, one axon
- unipolar: no dendrites, one axon
- anaxonic: many dendrites, but NO axon
universital properties of a neruon
- excitability (irritability): can respond to stimuli
- conductivity: can send signals to distant locations quickly
- secretion: can release chemical messengers (neurotransmitters)
parts of a neuron
- neurosoma (soma or cell body): control center
- nissl bodies: compartmentalized rough endoplasmic reticulum
- dendrites: recieve signals
- axon: sends signals
- terminal arborization: complex branches at axon’s distal end
- synaptic knob (terminal button): ending of axon branch that communicates with another cell
nissl bodies of a neuron
compartmentalized RER
myelin of a neuron
A layer of fatty tissue encasing the fibers of many neurons
conductivity of a neuron
can send signals to distant locations quickly
neurotransmitters
can send signals to distant locations quickly
types of neuroglia (glial cells)
CNS glia:
- oligodendrocytes myelinate to assist conduction
- ependymal cells secrete and circulate CSF
- microglia help in defense and disposal
- astrocytes provide support and noursishment
PNS glia:
- schwan cells myelinate to assist conduction
- satellite cells provide support and nourisment
Myelin
- like insulation on a wire
- oligodendrocytes make fatty white matter of CNS
internodes
fiber segments covered by myelin
nodes of ranvier
fiber segments with gaps in myelin
myelination
the neurilemma is the outmost coiled layer of a schwann cell
unmyelinated nerve fibers
even unmyelinated PNS axons are surrounded by schwann cells but the schwann cells do not coil densely around these axons
signal conductuction
speed depnds on:
- diameter of fiber: largere are faster
- presence of myelin: myelinated are faster
fastest fibers for signal conduction
large in diamter and have myelin
nerve regeneration
- if cell body remains intact, cut nerve fibers can regenerate
- schwann cells secrete nerve growth fibers
- schwann cells and endoneurium produce regeneration tube to direcr regrowth of axon
- CNS neurons CANNOT regenerate
synapse
- meeting point of neuron and other cell
- presynaptic neuron to post synaptic neuron
structure:
- synaptic knob of presynaptic cell: contains synaptic vesicles (packets of neurotransmitters)
- synaptic cleft
- neurotransmitter receptors on postsynaptic cell
types of synapses
- axodendritic synapse: axon to dendrite
- axosomatic synapse: axon to soma
- axoaxonic synapse: axon to axon
chemical synapse
- presynaptic neuron releases neurotransmistters to postsynaptic cell
- neurotransmitters: messenger molecules (some excite, some inhibit)
electrical synapse
- adjacent cells joined by gap junctions
- ions diffuse from cell to cell
- quick transmission
- no integration or decision making
spinal cord functions
conduction:
- sensory information ascends
- motor commands descend
neural integration:
- processing of info from diverse sources
locomotion:
- central pattern generators coordinate simple repetitive movements
reflexes:
- involuntary sterotyped responses to stimuli
meninges
3 layers of membranes protect the brain and spinal cord:
- dura matter
- arachnoid matter
- pia matter
dura matter
- tough, outer later
- dural sheath: an extension of the dura mater that surrounds the spinal nerves of the spinal cord
within cranium, the dura has 2 layers:
- periosteal layer
- meningeal layer
in some places, the payers separate to form dural sinuses:
- superior sagittal siuns
- transverse sinus
in some places, dural sheets occupy spaces spearating major parts of the brain
- flax cerebri: between hemispheres
- tentorium cerebelli: between cerebrum and cerebellum
pia matter
- delicate, inner layer
- terminal filum
- coccugenal ligament
- denticulate ligaments
arachnoid matter
- transparent, middle layer
- simple squamous
- subarachnoid space: contains cerebral spinal fluid and lumbar cistern
gray matter structure
- contains little myelin
- 2 posterior (dorsal) horns
- 2 anterior (ventral) horns
- 2 lateral horns with thoracic and lumbar regions
white matter structure
- contains myelin
- 3 pairs of columns (funiculi) containing tracts (fasciculi) : posterior (dorsal), lateral, and anterior (ventral) columns
- tracts: bundles of myelinated axons
spinal tracts
ascending tracts carry sensory info to brain, whereas descending tracts carry motor info from brain
many tracts cross the midline at a decussation:
- tract origin is contralateral to its destination
- thus a right brain stroke impairs left side of body’s function
some tracts do not cross the midline:
- the tract origin is on the same side of the body (ipsilateral) to its destination
ascending spinal tracts
sensory pathways contain first-, second-, and third-order nerve fibers
2 tracts ascend within each posterior funiculus to end in the medulla:
- gracile functions: from lower body
- cuneate fasciculus: from upper body
both of these posterior funiculus tracts contain first order neurons sensing body position, discriminative touch, and pressure on the same side of body
the spinothalamic tract ascends in the anterior and lateral funiculi to end in the thalamus
- this tract contains second order neurons sensing pain and temperature from contralateral sensory neurons
ascending tracts of the CNS example
- the posterior column: medial lemniscus pathway decussates in the medulla
- the spinothalamic pathway: decussates in the spinal cord
descending tracts
- motor pathways contain upper and lower motor neurons
- corticospinal tracts carry signals for precise limb movemnts from motot cortex (upper motot neurons): lateral and anterior corticospinal tract
upper motor neurons
lower motor neurons
corticospinal tracts
- lateral corticospinal tract: large pathway in lateral column
- anterior corticospinal tract: small pathway in anterior column
2 descending tracts of the CNS
- lateral corticospinal fibers: decussate in the medulla
- anterior corticospinal fibers: decussate in the spinal cord
anatomy of a nerve
nerve- several axons wrapped by connective tissue:
- endoneurium: wraps one axon
- perineurium: wraps a fascile of axons
- epineurium: wraps entire nerve
afferent fibers
carry sensory signals from receptors to the CNS
efferent fibers
carry motot signals from CNS to effectors
somatic fibers
supply skin, skeletal muscle, bones, and joins
visceral fibers
supply blood vessles, glands, and viscera
general fibers
supply widespread organs such as muscles, skin, glands, viscera, and blood vessels
special fibers
supply more localized organs in the head like eyes, ears, olfactor and taste receptors, and muscles of chewing, swalling, and facial expression
ganglion
a cluster of cell bodies outside the CNS
spinal nerves
proximal branches:
- dorsal root and dorsal root ganglion
- ventral root
distal branches:
- posterior ramus
- anterior ramus: in thorax it becomes intercostal nerve; in other regions it helps make a plexus
- meningeal branch
nerve plexuses
plexuses recieve nerve fibers from anterior rami and give rise to peripheral nerves:
- cervical plexus: in neck
- brachial plexus: in shoulder
- lumbar plexus: in lower back
- sacral plexus: below lumbar
- coccygeal plexus: lower scarum and coccyx
somatic reflexes
- skeletal muscles
- controlled by somatic nervous system
properties of somatic reflexes:
- requires stimulation
- quick
- involunatry
- sterotyped
visceral refex
- glands, cardiac muscle, smooth muscle
- controlled by ANS
components of reflex arc
- somatic receptors
- afferent nerve fibers
- integrating center
- efferent nerve fibers
- skeletal muscles
ipsilateral reflex
general reflex category
CNS output and input on same side
contralateral reflex
general reflex category
sensory output from opposite side as motor output
intersegmental reflex
general reflex category
sensory signal in one level; motor noutput at a higer or lower level
cerebrum
- 2 cerebral hemispheres
- gyri: folds
- sulci: grooves
- longitudinal cerebral fissure: big sulcus between hemispheres
cerebellum
- gyri: folds
brainstem
- crucial for survival
gray matter locations
- superficial on brain
- outer part (cortex) of cerebrum and of cerebellum, as well as deep nuclei
- neurosomas (cell bodies), dendrites, and synapses
white matter locations
deep in brain
ventricles
- lateral ventricle: interventricular foramen
- third ventricle: cerebral aqueduct
- fourth ventricle: central canal and choroid plexus
cerebrospinal fluis (CSF)
- clear, colorless liquid
- produced by choroid plexus within ventricles
- flows within ventricles, canals, and subarachnoid space around CNS
- absorbed by arachnoid granulation into blood of superior sagittal sinus
- provides buoyancy, protection, and chemical stability
blood supply
brain is only 2% of body weight but recieves 15% of blood and uses 20% of oxygen and glucose
blood-brain barrier (BBB)
- seals capillaries in brain tissue
- tight junctions between endothelial cells
blood-CSF barrier
- seals choroid plexus within brain ventricles
- tight junctions between ependymal cells
circumventricular organs (CVO)
- regions of 3rd and 4th ventricles that lack BBB
- allow brain to monitor blood chemistry
medulla oblongata function
- origin or termination of cranial nerves IX, X, and XII and some fibers of VIII
- sensory nuclei receive input from the taste buds, pharynx, and thoracic and abdominal viscera
- motor nuclei include the cardiac center (adjusts the rate and force of the heartbeat), vasomotor center (controls blood vessel diameter and blood pressure), two respiratory centers (control the rate and depth of breathing), and centers involved in speech, coughing, sneezing, salivation, swallowing, gagging, vomiting, sweating, gastrointestinal secretion, and movements of the tongue and head.
medualla oblongata structure
- developes from myelencephalon
- extends from foramen magnum to pons
important nuclei of medualla oblongata
- cardiac center
- vasomotor center
- respiratory center
anterior surface buldges of medualla oblongata
- pyramids (medial)
- olives (lateral)
internal structures of medualla oblongata
- corticospinal tracts: pyramidal decussation
- inferior olivary nucleus
- reticular formation
- gracile and cuneate nuclei: medial lemniscus
- tectospinal tract
- posterior spinocerebellar tract
- foruth ventricle
- cranial nerves VIII, IX, X, XI
pons functions
- sensory terminations and motor origins of cranial nerves V–VII and some fibers of VIII
- sensory nuclei receive input from the face, eyes, oral and nasal cavities, sinuses, and meninges, concerned with pain, touch, temperature, taste, hearing, and equilibrium
- cranial nerve motor nuclei control chewing, swallowing, eye movements, middle- and inner-ear reflexes, facial expression, and secretion of tears and saliva
- other nuclei of pons relay signals from cerebrum to cerebellum (provide most of the input to the cerebellum) or function in sleep, respiration, bladder control, and posture
pons structure
- developed from metencephalon
- anterior aspect: large buldge
- posterior aspect: peduncles that attach to cerebellum
- internally, contains parts of several tracts and nerves: medial lemniscus, tectospinal tract, anterolateral system, anterior spinocerebellar tract, cranial nerves (V-VIII)
midbrain functions
- origin of cranial nerves lll–IV (concerned with eye movements). Red nucleus is concerned with fine motor control
- substantia nigra relays inhibitory signals to thalamus and basal nuclei of forebrain
- central gray substance modulates awareness of pain
- superior colliculi are concerned with visual attention and tracking movements of eyes, and visual reflexes such as shifting gaze to objects seen moving in peripheral vision
- inferior colliculi relay auditory signals to thalamus and mediate auditory reflexes such as the startle response to a loud noise
midbrain structure
- developes from mesencephalon
- cerebral aqueduct passes through: central (periaqueductal) gray matter
- gives rise to cranial nerves III and IV
posterior aspect of midbrain
tectum
- corpora quadrigemina: 4 bludge consisting of superior ajd inferior colliculi
anterior aspect of midbrain
cerebral peduncles
- tegmentum with red nucleus
- substantia nigra: degenerates into Parkinson’s
- cerebral crura anchor cerebrum into brainstem
reticular formation
- web of gray matter tht runs through all levels of brainstem
functions:
- somatic motor control
- equilibrium
- visual attention
- breathing
- swallowing
- cardiovasuclar control
- pain modulation
- sleep and consciousness
- habituation
cerebellum structure
- cerebellar hemispheres
- vermis
- cortex of folia amd sulci (gray matter): numerous granule cells and large Purkinje cells
- arbor vitae: white latter
- deep nuclei: gray matter
cerebellum functions
- muscular coordination
- fine motor control
- muscle tone
- posture
- equilibrium
- judging passage of time
- some involvement in emotion
- congitive functions: processing tactile input, spatial perception, and language
diencephalon
- part of the forbrain
- 3 divisions that surround the third ventricle: thalamus, hypothalamus, epithalamus
thalamus
- large ovoid mass that makes up 4/5th of diencephalon
- intermediate mass connects lefts and right thalami
- “gateway to the cerebral cortext”
thalamus functions
involved in sensation, movement, memory, and emotions
hypothalamus
- extends from optic chiasm to mammillary bodies
- major control center of the autonomic nervous system and endocrine system
hypotalamus functions
- hormone secretion
- autonomic effects
- thermoregulation
- food and water intake
- sleep and circadian rhythms
- emotion responses
- memory
epithalamus
- pineal gland: an endocrine glan
- habenula: relay from limbic system to midbrain
- thin roof over the third ventricle
cerebrum
- derived from embryonic telencephalon of forebrain
- cerebrfal hemispheres are separated by longitudinal fissu and connected by corpus collasum
- gyri and sulci produce large surface area
frontal lobe of the cerebrum
- location: from frontal bone to central sulcus
- function: cognition, speech, and motor control
parietal lobe of the cerebrum
- location: from central sulcus to parieto-occipital sulcus
- function: interprets signals of general senses and taste
occipital lobe of the cerebrum
- location: from parieto-occipital sulcus to occipital bone
- function: principal visual center
temporal lobe of the cerebrum
- location: from temporal bone to lateral sulcus
- function:hearing, smell, learning, and memeory
insula of the cerebrum
- location: deep to lateral sulcus
- function: taste, visceral sensation, and language
cerebral white matter
tracts: bundles of myelinated axons
- projection tracts
- commissural tracts
- association tracts
projection tracts
travel vertically to carry info between cerebrum and rest of body
commissural tracts
- commissures cross between 2 hemispgeres
- corpus callosum is largest
association tracts
- connects regions within same hemisphere
cerebral cortex
- surface of the hemmispheres
- 40% of mass of brain
- contains stellate cells and pyramidal cells
- neocortex: 6 layers “recently” evolved
stellate cells
cereebral cortex
- severeal short dendrites, no axon
- local processing of sensory info
pyramidal cells
- triangle shaped with apex pointing to brain surface
- output neurons of cerebrum
limbic system functions
emotions and learning
prominent parts of the limbic system
- cingulate gyrus, hippocamous, and amygdala
- contains multiple gratification and aversion centers
basal nuceli
- deep masses of cerebral gray matter
- consist of caudate nucleus, putamen, and globus pallidus
- function: involved in motor control
primary cortex
integrative brain functions
- primary sensory cortex is first cortical region to percieve input for that issue
- primary motor cortex issues projection fibers to distribute motor commands
association cortex
integrative brain functions
- any cortical area that is not primary
- interpretation of sensations, thought, memory, and motor planning: prefrontal cortex
brain region for vision
- occipital lobe
- primary visual cortex
brain region for hearing
- temporal lobe and insula
- primary auditory cortex
brain region for equilibrium
- cerebellum
- several brainstem nuclei
brain region for taste
- parietal lobe
- primary gustatory cortex
brain region for smell
- temporal and frontal lobes
- orbitofrontal cortex
primary somatosensory cortex
- postcentral gyrus
- exhibts somatotopy: a body map
primary motor cortex
- precentral gyrus
- contains upper motor neurons that control contralateral muscles
wernicke area
- posterior to lateral sulcus of left brain
- recognition of written and spoken language
language processing areas
- wernicke area
- broca area
broca area
- inferior prefrontal cortex of left brain
- speech
emotion
- several areas involved
- amygdala outputs to hypothalamus and prefrontal cortex
cognition
- acquire and use knowledge
- association areas of cortex
memory
2 types:
- procedural
- declarative
limbic areas involved:
- amygdala creates emotions memories
- hippocampus consolidates declarative long-term memories
cerebral lateralization
- difference in function for each hemisphere
- categorical hemisphere
- representation hemisphere
olfactory nerve (I)
cranial nerves
sensory nerve for smell
optic nerve (II)
cranial nerves
sensory nerve for vision
oculomotor nerve (III)
cranial nerves
motot nerve for eye movement
trochlear nerve (IV)
cranial nerves
motor nerve for eye movement
trigeminal nerve (V)
cranial nerves
mixed nerve for sensation of the face and control of chewing movements
abducens nerve (VI)
cranial nerves
motor nerve for eye movement
facial nerve (VII)
cranial nerves
mixed nerve for sensation of taste and control of expression, facial secretions
vestibulocochlear nerve (VIII)
cranial nerves
sensory nerve for hearing and equilibrium
glossopharyngeal nerve (IX)
cranial nerves
mixed nerve with diferse sensory and motor functions for head, neck, and thorax
vagus nerve (X)
cranial nerves
mixed nerve for taste, gastrointestinal sensation, and control of various organs
accessory nerve (XI)
cranial nerves
motor nerve for swallowing, head, neck, and shoulder movements
hypoglossal nerve (XII)
cranial nerves
motor nerve controlling movements of tongue
actions of the autonomic nervous system (ANS)
- visceral motor system- in contrast to somatic motor system
- involuntary control of glands, cardiac muscle, and smooth muscle (ANS not required for effector activity, but ANS modulates the activity)
- responsible for visceral reflexes
visceral reflexes
- unconscious, automatic, sterotyped respnses of visceral effectors to stimuli
- ex: a rise in blood pressure triggers a reflexive decrease in heart rate
divisions of the ANS
- sympathetic division
- parasymathetic division
- autonomic tone
sympathetic division of ANS physiological response
- fight or flight responses for increased physical activity
- increases heart rate and blood glucose
- reduces blood flow to skin and GI tract
parasympathetic division of ANS physiological response
- rest and digest responses with calming effects
- decreases heart rate
- stimulates digestion and waste elimination
autonomic tone of ANS
balance between activity of sympathetic and parasympathetic tone
neural pathways of ANS
preganglionic neuron:
- soma in brainstem or spinal cord
- axon terminates in ganglion
postganglionic neuron:
- soma in ganglion
- axon extends to target
sympathetic division
- aka thoracolumbar division
- preganglionic somas are in lateral horns
- short preganlionic fibers, long postganglionic fibers
- sympathetic chain ganglia (paravertebral ganglia) from cervical to coccygeal levels
sympathetic division preganglionic fibers
enter ganglia through white communicating rami
sympathetic divison postganglionic fibers
- unmyelinated
- leave ganglia by various routes including gray communicating rami
sympathetic division spinal nerve route
- the preganglionic fiber synapses in a sympathetic chain ganglion, and travels via a gray communicating ramus to a spinal nerve.
- the postganglionic fiber travels with the spinal nerve to target organs in the range of distribution of the nerve.
- effectors in the limbs and body wall are mainly innervated by sympathetic fibers in spinal nerves.
- ex: sweat glands, piloerector muscles, and blood vessels of the skin and skeletal muscles.
sympathetic division sympathetic nervous route
- sympathetic nerves travel from ganglia directly to the heart, lungs, esophagus, and structures in the head.
- these are areas that cannot be reached by “hitching a ride” on a spinal nerve
sympathetic division splanchnic route
- splanchnic nerves innervate structures in the abdominal cavity
- preganglionic fibers pass through chain ganglia without synapsing
- beyond the ganglia, they form greater, lesser, and lumbar splanchnic nerves, which lead to collateral (prevertebral) ganglia
- these include the celiac, superior mesenteric, and inferior mesenteric ganglia, located at points where arteries with the same names branch off the abdominal aorta
- the postganglionic fibers then travel with the arteries to target organs.
preganglionic sympathetic fibers
- myelinated
- travel from the spinal nerve to the sympathetic ganglion by way of a white communicating ramus
postganglionic sympathetic fibers
- unmyelinated
- leave the ganglion through a gray communicating ramus that returns to the spinal nerve, or through sympathetic nerves that lead to target organs of the head and thorax.
splanchnic nerves
- sympathetic fibers that pass through the ganglia without synapsing
- travel to synapses in the ganglia of the abdominal aortic plexus
adrenal glands
- located atop each kidney
- adrenal cortex (outer part): secretes steriod hormones
- adrenal medulla (inner part): secretes epinephrine, norepinephrine- modified sympathetic ganglion
parasympathetic division
- aka craniosacral division because it arises from the brain and the sacral region of the spinal cord
- long preganglionic fibers through cranial nerves III, VII, IX, and X, and spinal nerves S2 through S4, to their target organs
- very short postganglionic fibers
- more selective in its stimmulation of target organs
- innervation to head: Oculomotor nerve (III), Facial nerve (VII), Glossopharyngeal nerve (IX)
- innervation to viscera: vagus nerve (X)
4 cranial nerves that carry parasympathetic fibers
- CN III Oculomotor n. controls lens and pupil
- CN VII Facial n. controls tear, salivary, nasal glands
- CN IX Glossopharyngeal n. controls salivary glands
- CN X Vagus n. provides branches for heart, lungs, esophagus and other organs: contains 90% of parasympathetic preganglionic fibers
