chapter 19 - nervous system

central nervous system (CNS)

brain and spinal cord

• functions to process and integrate info

peripheral nervous system (PNS)

• nerves originate from the brain (cranial) and spinal cord (spinal)

• nerves detect changes in the surrounding environment → stimuli (awareness)

  • information is transmitted to CNS for processing

division of the PNS

sensory and motor

division of the motor division of the PNS

somatic and autonomic

impulses

electrical signals that are generated as a result of nervous system stimulation

stimuli

a change in internal/external environment of the body

glial cells

cells in the nervous system that function to support the neurons

• capable of mitosis

• 85% of all cells in the brain

astrocyte

star-shaped glial cells in the CNS that forms a portion of the blood-brain barrier

microglia

glial cells in the CNS that function in protection against infection, becoming phagocytic

ependymal cells

glial cells in the CNS that line cavities in the CNS, ventricles, and spinal canal; secrete and circulate cerebrospinal fluid

oligodendrocytes

glial cells in the CNS that function to produce myelin sheath

schwann cells

glial cells in the PNS that produce myelin sheaths

satellite cells

glial cells in the PNS that are found around neuronal cell bodies in the ganglia; function in support

neurons

cells that function to integrate and store information

• conduct electrical impulses

• ~15% of total brain cells

• incapable of mitosis

cell body

part of a neuron that contains typical cellular organelles with the exception of centrioles bc they don't complete mitosis

nissl bodies

rough endoplasmic reticulums in neurons

dendrites

short, branching projections into the cell body

• receive incoming messages and relay them to the cell body to be processed and interpreted

axon

structure that extends from the cell body

• may be myelinated or unmyelinated

• can be long (up to metres) or short

• generates and transmits nerve impulses

• ends at the “axon terminal” — contains synaptic end bulbs

axon hillock

where the axon joins the cell body

myelinated axon sheaths

axon sheaths that are wrapped by many layers of the cell membrane called “myelin”

tracts

myalinated neurons in the CNS

nerves

myalinated neurons in the PNS

nodes of ranvier

gaps in the myelin along the length of the axon

multipolar neuron

a neuron with many processes extending from the cell body

• one axon and many dendrites

• interneurons and motor neurons

bipolar neuron

a neuron with two processes extending from the cell body

• one axon and one dendrite

• sensory neurons for sight and olfaction

unipolar neuron

a neuron with one process extending from the cell body

• one process which divides into peripheral and central processes — one long horizontal piece

• always sensory neurons

afferent/sensory neurons

neurons that move collected impulses from sensory receptors toward the CNS

• unipolar neurons

efferent/motor neurons

neurons that move impulses from the CNS into effector cells

• multipolar neurons

interneurons

neurons in between sensory and motor neurons, and transmit impulses within the CNS

• 99% of neurons in the body — most are multipolar

neuronal synapses

synapses between 2 neurons

• can be chemical or electric

neuromuscular junction

synapses between a motor neuron and sarcolemma of a skeletal muscle cell (fiber)

neuroglandular junction

synapses between a motor neuron and a gland

chemical synapses

most common type of neuronal synapses

pre-synaptic neuron

a neuron that brings in the signal

• contains an axon terminal with synaptic end bulbs

• these bulbs contain neurotransmitters → chemical messengers, released upon a stimulus

post-synaptic neuron

a neuron that receives the signal

• dendrites are the particular area that receive the signal

• membrane contains specific receptors for the neurotransmitter that was released

gray matter

composed of an aggregation of neural cell bodies and dendrites

neclei

clusters of neural cell bodies in the CNS

ganglia

clusters of neural cell bodies in the PNS

white matter

composed of axons that are myelinated

tracts

bundles of myelinated axons in the CNS

nerves

bundles of myelinated axons in the PNS

meninges

connective tissue membranes that surround the brain and spinal cord

1. dura mater

   • 2 layers in the brain, mostly fused

   • 1 layer in the spinal cord

2. arachnoid mater

   • beneath the dura mater

   • avascular

3. pia mater

   • vascular

   • directly on top of the brain and spinal cord

dural sinuses

spaces between the 2 layers of the dura mater of the brain

• filled with venous blood

epidural space

the space between the dura mater and vertebral canal; filled with connective tissues, fat, and vasculature

subdural space

the space between the dura mater and arachnoid mater; filled with interstitial fluid

arachnoid villi

projections of the arachnoid mater in the brain into the dural sinuses to deliver CSF into the blood

subarachnoid space

the space between the arachnoid and pia mater, filled with CSF

meningitis

the inflammation of the meninges

cerebrospinal fluid (CSF)

fluid that's located in and around the CNS

• similar composition to blood plasma

• provides insulation to the brain and allows the brain to float within the cavity, reducing its weight

• replenished all the time

choroid plexuses

blood vessels of the brain’s ventricles that produce CSF

ventricles in the braian

• (2) lateral ventricles in the cerebrum

• (1) third ventricle in the diencephalon

• (1) fourth ventricle in the hindbrain

hydrocephalus

a condition that results from an accumulation of fluid in the ventricles of the brain

• occurs bc the cerebral aqueduct becomes blocked

• causes damage to brain tissue

blood-brain barrier

a selective permeable barrier in the brain that is formed by capillaries with tight junctions between endothelial cells and astrocytes

• located throughout most parts of the brain

circle of willis

a circular blood vessel system located at the base of the forebrain that connects the major cerebral arteries, providing collateral circulation

forebrain

cerebrum and diencephalon

cerebrum

the largest portion of the brain

• consists of 2 hemispheres, each consist of 3 main regions

• consists of 5 lobes

lobes of the cerebrum

1. frontal → motor function

2. temporal → memory function

3. parietal → sensory function

4. occipital → visual function

5. insula → visceral (abdominal) function

fissures

deep grooves in the brain

longitudinal fissure

a fissure that divides the brain into left and right hemispheres

transverse fissure

a fissure that separates the cerebrum from the cerebellum

sulcus

shallow grooves in the brain

gyri

elevated folds located over most of the brain’s surface

• separated from one another by sulcus’

precentral gyrus

gyrus in frontal lobe

postcentral gyrus

gyrus in parietal lobe

central sulcus

sulcus that separates frontal from parietal lobe

lateral sulcus

sulcus that separates temporal lobe from remainder of cerebrum

main regions of each hemisphere

1. cerebral cortex

   • gray matter visible on the surface of the brain

   • 2-4mm thick

   • contains 3 functional areas

2. white matter

   • composed of myelinated axons

   • have tracts

3. basal nuclei

   • paired masses of gray matter

   • located in the white matter of the cerebrum

   • function to modify skeletal muscle movements

functional areas of the cerebral cortex

1. motor area

   • located in the frontal lobe

   • controls skeletal muscle movement

   • primary area → on precentral gyrus

   • premotor area → anterior to precentral gyrus

     • plans movement, sends to primary area to be put in action

   • broca’s area → controls speech muscles

     • found only in one hemisphere

2. sensory area

   • processes sensory info

   • general sensory area → in postcentral gyrus, in the parietal lobe

     • pain, temperature, touch, and pressure (awareness)

   • specialized senses:

     • vision → occipital lobe

     • auditory and olfactory → temporal lobe

     • taste → insular lobe

     • visceral sensations → insular lobe

       • ex. full bladder

3. association area

   • located in parietal, occipital, and temporal lobes

   • allows recall/recognition of info store in memory → temporal lobe

     • associating things/memories

   • intellect → frontal lobe

association tracts

tracts that transmit info from gyrus to gyrus within the same hemisphere

commissural tracts

tracts that transmit info from gyrus to gyrus in opposite hemispheres

• ex. corpus callosum

projection tracts

tracts that transmit info from the brain to the spinal cord, vice versa

• run vertically

diencephalon

thalamus and hypothalamus

thalamus

a part of the diencephalon that is located superiorly to midbrain

• relay center for most sensory impulses that are headed to the cortex for processing

intermediate mass

a bridge of gray matter that connects 2 lobes to form the thalamus

hypothalamus

a part of the diencephalon that is located inferior to the thalamus and superior to the pituitary gland

• composed of gray matter

• major regulator of internal environment

  • ex. blood pressure, heart rate

• has both endocrine and nervous function

midbrain

connects the pons and diencephalon

cerebral peduncles

projection tracts on the anterior portion of the midbrain

corpora quadrigemina

paired structures located on the posterior portion of the midbrain, involved in visual and auditory processing

superior colliculi

2 superior nuclei of the corpora quadrigemina

• control visual reflexes that allow the movement of the head and eyes, in response to visual stimuli

inferior colliculi

2 posterior nuclei of the corpora quadrigemina

• control auditory reflexes

• relay center for impulses that arise at the receptors → transmitted to auditory center

cranial nerves in midbrain

• oculomotor (III)

• trochlear (IV)

hindbrain

pons, medulla oblongata, cerebellum

pons

part of the hindbrain that is located anterior to the cerebellum

• connects the medulla to the midbrain

• contains tracts between the brain and spinal cord

• home to the “pontine respiratory center” → pontine nuclei

  • assists the medulla in maintaining normal breathing rhythms

cranial nerves in the pons

• trigeminal (V)

• abducens (VI)

• facial (VII)

medulla oblongata

part of the hindbrain that begins at the foramen magnum and blends into spinal cord

corticospinal tracts

large motor tracts (two pyramids) in the medulla oblongata

• ducussate (cross) just prior to the start of the spinal cord — to opposite sides of the body

• reason that each side of the brain controls opposite sides of the body

brainstem

midbrain + pons + medulla

cranial nerves in the medulla

• glosspharyngeal (IX)

• vagus (X)

• accessory (XI)

• hypoglossal (XII)

vital centers in the medulla

• cardiac → adjusts the force of contraction and heart rate

• vasomotor → adjusts blood vessel diameter

• respiratory → works with the pontine nuclei to control the rate and depth of breathing

non-vital centers in the medulla

• swallowing

• coughing

• vomitting

• sneezing

cerrebellum

part of the hindbrain that is located on the dorsal portion of the brain — posterior to the pons and medulla

• cortex is formed from gray matter

• functions to regulate:

  • skeletal muscle contraction

  • posture — knees, joints

  • balance

folia

folds in the cerebellum

arbor vitae

white matter deep within the cerebellum

limbic system

functional system in the brain that regulates emotions and emotional behaviours

• network of nulcei located in the cerebral hemisphere and diencephalon

reticular formation

functional system in the brain that keeps the individual alert and attentive

• nuclei located in the brainstem

• inhibition of this area → sleep

• damage to this area → coma

• many anesthetics and sleeping pills affect this area

• work with visual + environmental cues

spinal cord

begins below the foramen magnum and terminates in the lumbar region of the spinal column (L1/L2)

• contains cervical, thoracic, lumbar, and sacral segments that correspond to the vertebral sections

• functions to take in sensory info and generate motor output

  • also generates reflexes

• cross-sectionally, it’s separated into right and left halves by:

  • anterior median fissure → ventral side

  • posterior median sulcus → dorsal side

  • central canal → middle

conus medullaris

cone-shaped termination region of the spina cord

cauda equina

nerves that exit below the conus medullaris that resembles a horse's tail

filum terminale

anchors the conus to the coccyx; formed from connective tissue that’s an extension of the pia mater

gray commissure

the crossbar of the H-shaped gray matter of the spinal cord