Course Exam 3 Flashcards
What are the four principle function of the spinal cord?
1. Conduction - information sent up and down via electrical signals (between sensors, control center CNS and effectors
2. Neural Integration - Nerves receive information from multiple locations and they integrate
3. Locomotion - walking involves several muscles and neurons
4. Reflexes - integration- vital role in posture, motor control and response to pain
What are the regions the spinal chord is divided into?
cervical
thoracic
lumbar
sacral
In two areas the cord is a little thicker than eleswhere. What are these regions called?
In the inferior cervical region = cervical enlargement
lumbosacral region = lumbar enlargement
where does the cord taper to a point?
medullary cone (conus medullaris)
What is the bundle of nerve roots that occupy the vertebral cone from L2 to S5?
cauda equina
(resemblance of a horse’s tail)
Innervates the pelvic organs and lower limbs
What is the fiberous (3) membranes that enclose the spinal cord and brain called?
meninges
separate the soft tissue of the central nervous system from the bone of the vertebrae and skull
from superficial to deep, they are the dura mater, arachnoid mater and pia mater
What forms a loose-fitting sleeve around the spinal cord?
What is the sleeve called as well?
dura mater
- keeps other things separated from the spinal cord (Epidurals go into this outer dura mater)
dural sheath
What is the space between the sheath and vertebral bone called?
epidural space
occupied by bone vessels, adipose tissue, and loose connective tissue
location of the epidural anesthesia during childbirth
What consists of a highly vascular layer and a simple squamous epithelium that adhears to the inside of the dura, and a loose mesh of collagenous and elasic fibers
arachnoid mater
- does not preserve very well…
What gap is filled with cerebrospinal fluid (CSF)
subarachnoid space
What is inferior to the medullary cone, the subarachnoid space called? is occupied by the cauda equina and CSF
lumbar cistern
What is delicate, transparent membrane that closely follows the contours of the spinal cord
pia mater
What is relatively dull color because it contains little myelin - mainly neural cell bodies?
contains the somas, dendrites and proximal parts of the axons of neurons
The site of synaptic contact between neurons and therefore the site of all neural integration in the spinal cord
Gray matter
What is bright, pearly white appearance due to the abundance of myelin.
It is composed of bundles of axons, called tracts, that carry signals from one level of the CNS to another
White matter
What are two directional terms used in descriptions of CNS anatomy?
Name and describe
Rostral = “toward the nose”
caudal = “toward the tail”
What are the three major portions to divide the brain?
Cerebrum = 83% of brain’s volume and consists of a pair of half globes called the cerebral hemispheres
Cerebellum = occupies the posterior cranial fossa inferior to the cerebrum, separated from it by the transverse cerebral fissure
Brainstem = it is all of the brain except the cerebrum and cerebellum. Its major components, from rostral to caudal, are the diencephalon, midbrain, pons, and medulla oblangata
What is the thick folds that divide the brain?
What are the thick folds separated by with shallow grooves called?
Thick folds = gyri
Shallow grooves = sulci
What are the thick bundle of nerve fibers that are at the bottom of the fissure that connect the hemispheres?
corpus callosum
a prominent landmark for anatomical description with a distinctive C shape in sagittal section
What is the cerebellum separated by?
transverse cerebral fissure
What are the major components of the brainstem?
diencephalon, midbrain, pons, and medulla oblangata
What does the seat of the neurosomas, dendrites and synapses (gray matter) forming a surface layer called?
cortex
over the cerebrum and cerebellum, and deeper masses called nuclei surrounded by white matter
As in the spinal cord, white matter of the brain is composed of what?
tracts, or bundles of axons, which here connect one part of the brain to another and to the spinal cord
What does the nervous system develop from?
ectoderm, the outermost tissue layer of an embryo
When does the nervous system develop?
Within the first 3 weeks, a neural plate forms along the dorsal midline of the embryo and sinks into the tissues to form a neural groove, wich a raised neural fold along each side.
What occurs on day 26?
Creates a hollow channel called the neural tube. Following closure, the neural tube separates from the overlying ectoderm, sinks a little deeper, and grows lateral processes that later form motor nerve fibers
As the neural tube develops, some ectodermal cells that originally lay along the margin of the groove separate from the rest and form a longitudinal column on each side called this?
neural crest
give rise to the two inner meninges (arachnoid mater and pia mater); most of the peripheral nervous system, including the sensory and autonomic nerves and ganglia and schwann cells; and some other structures of the skeletal, integumentary, and endocrine systems
What are the neural tube exhibits three anterior dilations, or primary vesicles called?
forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon)
By the fifth week, it subdivides into five secondary vesicles. The forebrain divides into two of them, what are they?
telencephalon and diencephalon
By the fifth week, it subdivides into five secondary vesicles. The midbrain remains undivided and retains the name?
mesencephalon
By the fifth week, it subdivides into five secondary vesicles. The hindbrain divides into two of them, what are they?
metencephalon
myelencephalon
What are the three connective tissue membranes that envelope the brain?
meninges lie between the nervous tissue and bone made up from:
dura mater
arachnoid mater
pia mater
What is the function of the meninges (made of 3 layers)
Protect the brain and provide a structural framework for its arteries and veins
In the cranial cavity, the dura mater consists of two layers?
an outer periosteal layer equivalent to the periosteum of the cranial bones, and an inner meningeal layer
Only the meningeal layer continues into the vertebral canal, where it forms the dural sheath around the spinal cord
In some places, the two layers of dura are separated by?
dural sinuses, spaces that collect blood that has circulated through the brain
Two major, superficial ones are the superior sagittal sinus, found just under the cranium along the median line, and the transverse sinus, which runs horizonatally from the rear of the head toward each ear.
These sinuses meet like an inverted T at the back of the brain and ultimately empty into the internal jugular veins of the neck.
The brain has four internal chambers called?
ventricles
What is the largest and most rostral internal chamber of the brain
two lateral ventricles, which form an arc in each cerebral hemisphere
Through a tiny pore called the _________ _________, each lateral ventricle is connected to the _____ _____, a narrow median space inferior to the corpus callosum.
interventricular foramen
third ventricle
From here, a canal called the ____ _____ passes down the core of the midbrain and leads to the _____ _____, a small triangular chamber between the pons and cerebellum.
Cerebral aqueduct
fourth ventricle
Caudally, this space narrows and forms a _____ ______ that extends through the medulla oblongata into the spinal cord
central canal
on the floor or wall of each ventricle is a spongy mass of blood capillaries called?
choroid plexus
named for its histological resemblance to a fetal membrane called the chorion
What is the clear, colorless liquid that fills the ventricles and canals of the CNS and bathes its external surfac?
Cerebrospinal fluid (CSF)
Explain the movement of cerebrospinal fluid (CSF)
The brain produces ~500 ml of CSF/day, but the fluid is constantly reabsorbed at the same rate and only 100 - 160 mL is normally presented at one time.
~40% is formed in the subarachnoid space external to the brain, 30% by the general ependymal lining of the brain ventricles, and 30% by the choroid plexuses.
How is CSF produced and what does it compose of?
Begins with the filtration of blood plasma through the capillaries of the brain
Ependymal cells modify the filtrate as it passes through them, so the CSF has more sodium and chloride than blood plasma, but less potassium, calcium, and glucose and very little protein
What is the hydrocephalus?
The abnormal accumulation of CSF in the brain, usually resulting from a blockage in its route of flow and reabsorption. Such obstructions occur most commonly in the interventricular foramen, cerebral aqueduct, and apertures of the fourth ventricle. The accumulated CSF expands the ventricles and compresses the nervous tissue, with potentially fatal consequences. In a fetus or infant, it can cause the entire head to enlarge because the cranial bones are not yet fused. Good recovery can be achieved if a tube (shunt) is inserted to drain fluid from the ventricles into a vein of the neck.
CSF is reabsorbed by ______ _______, extensions of the arachnoid meninx shaped like little sprigs or cauliflower, protruding throug the dura mater into the superior sagittal sinus.
arachnoid granulations
CSF penetrates the walls of the granulations and mixes with blood in the sinus.
Cerebrospinal fluid sereves three main purposes
name and describe
- Buoyancy - Because the brain and CSF are similar in density, the brain neither sinks nor floats in the CSF. It hangs from delicate specialized fibroblasts of the arachnoid meninx. A human brain removed from the body weighs about 1,500 g, but when suspended in CSF its effective weight is only about 50 g.
- Protection
- Chemical stability
Despite its critical importance to the brain, blood is also a source of this?
antibodies, macrophages, bacterial toxins, and other potentially harmful agents
What protects the brain and strictly regulates what can get from the bloodstream into the tissue fluid of the brain
Brain barrier system
There are two poteintial points of entry that must be gaurded, what are they?
the blood capillaries throughout the brain tissue and the capillaries of the choroid plexuses
What type of protection is consists of tight junctions between the endothelial cells that form the capillary walls
blood-brain barrier (BBB)
What are the types of ascending tracts?
- Gracile Fasciculus
- Cuneate Fasciculus
- Spinothalamic
- Spinoreticular
- Spinocerebellar
‘Big Picture’
What makes up the peripheral nervous system?
Nerves and ganglia
‘Big Picture’
What makes up the central nervous system?
Tracts and centers
What is the main organization of the ascending tracts?
Neural pathway:
- first : stimulus to spinal cord - balance (afferent neurons)
- Second : spinal cord to thalamus
- Third : Thalamus to cortex (sense large changes)
Explain the Gracile Fasciculus
Ascending Tract
- Somatic pathway
- Carries sensations of trunk position and movement, deep touch, visceral pain and vibration
- Below T6 to the thalamus
gracile = “thin and skinny”
What structure is an ascending tract that does the following:
- cone shaped
- Carries sensations of movement, deep touch, visceral pain and vibration
- above T6 to the thalamus
Cuneate Fasciculus
- somatic pathway
(Recall, above T6 is the arms)
Explain the Spinothalamic
Ascending Tract
- Somatic pathway
- Carries sensations of light touch, itch, temperature, pain and pressure
- to the thalamus
- connects the spine and the thalamus
What carries senesations of pain from injury to the thalamus?
Spinoreticular
- Ascending tract
- Somatic pathway
- Recall: reticular = net like
Explain the spinocerebellar
Ascending Tract
- Somatic Pathway
- Carries information on muscle positions (proprioception) to the cerebellum
- No third order neuron, we do not have a sense of this, it just does it
Name the descending tracts
Muscles of the face are innervated in before spinal cord
Vast majority in cerebral cortex
- Corticospinal
- Tectospinal
- Reticulospinal
- Vestibulospinal
What is the organization of the descending tracts?
ALL SOMATIC
- Upper motor neuron - originates in the brain (most thin little slice in cerebral cortex = motor cortex)
- Lower motor neuron - innervates muscles as part of NMJ
- Synapse at grey horns
Explain the Corticospinal tract
Descending Tract
- Somatic pathway
- Fine control of limbs
- Pretty large areas, lots of axons due to lots of potential movements
- cortico = cerebral cortex and spine, then leaves by peripheral nerves
What is responsible for reflexive head movement
Tectospinal
- Descending tracts
- Somatic pathway
- Maintains head posture
Explain the Reticulospinal tract
Descending Tracts
- Somatic pathway
- Balance and posture, regulation of awareness of pain
- Can modify how much pain gets in
- Reticular = net like
What tract is responsible for balance and posture (lateral) and control of head position (medial)
Vestibulospinal
- Descending Tracts
Somatic Pathway
Explain where spinal nerves originate and what they do
- Originate at spinal cord and axons go to somewhere else
- Carry sensory input and motor output
- LOCATION, LOCATION, LOCATION
What is the region of skin innervated by sipinal nerves called?
Dermatomes
- can be used to locate spinal damage
- Knowing where the nerves run you can diagnose where the pain or injury is
- Above T6 = okay to move carms but paralized legs
What are the properties of reflexes, specifically somatic reflexes?
- Require stimulation
- Rapid (not many neurons involved)
- Involuntary (Cannot control them but can modify them consciously)
- Non-variable
Explain the reflex arc
Homeostatic feedback loop - sorta negative
- Stimulus
- Sensory neuron activation (afferent neuron)
- Integration by interneuron (s) - location in the CNS, not brain
- Motor neuron activation - Stimulus directly activates action to reach threshold potential
- Effector response - only activates if large enough stimulus
(recall: action potentials are non variable)
What is a proprioceptor?
Muscle Spindle - Neuromuscular structure goes to cerebellum (balance/equilibrium)
- Give information on muscle position
- Intrafusal fiber: (intera = inside) the muscles that are doing the actual work - inside skeletal muscles (general tightness of sensor) - between the fibers
- Afferent neurons monitor rate of change (primary) and length (secondary)
- receptors to the brain how quickly = primary; what the actual length is right now =secondary neurons
What are the primary motor neurons responsible for?
Monitor rate of change
what are secondary neurons responsible for?
monitoring length that the muscle is currently at
What are the two types of motor neurons?
- Alpha : extrafusal fibers (NMJ) : the ones that contract the muscles
- Gamma : intrafusal fibers : Stimulate the sensor that allows for the muscle to be tight
What are the types of somatic reflexes?
- Stretch reflex
- Withdrawl reflex
- Crossed Extensor Reflex
- Tendon Reflex
Explain the stretch Reflex
As a muscle is stretched, tone increases
- maintains posture and balance, stabilizes movement
- Can involve multiple neurons, or as little as two
1. Monosynaptic reflexes: patellar reflex :
knee jerk reaction
Primary nerve: how rapid change
(temperal summation)
2. Polysynaptic reflexes: Involve more than one neuron and take more time (withdrawl reflex and crossed extensor reflex)
Sensory (afferent) and motor neurons (efferent) involved
Explain the withdrawl reflex
Stimlated by painful stimuli
Reciprical inhibition:
- Coontraction of agonists
- Relaxation of antagonists: potassium gates or chloride channels inhibit the muscles
Not only stimulate muscles to allow for a concertric activity, but also inhibits the muscles that do the opposit
Explain the crossed extensor reflex
Painful stimulus to foot while walking
- One side contraction of agonist, relaxation of antagonists
- Reversed on the other side
Still have more than one neuron acting together, but still a pretty simple reflux
One pulls away, other prepares for that by locking everything down for balance
What makes up the Diencephalon?
Three critical structures of the Diencephalon
- Epithalamus
- Thalamus
- Hypothalamus
What is the function of the Diencephalon?
Integration of conscious and unconscious sensory information and motor commands
What makes up the Epithalamus?
What part of the brain is the Epithalamus in?
Includes pineal gland (melatonin secretion)
Choroid plexus, Major lining of 3rd ventricle
Located in the Diencephalon
What is the function of the Thalamus?
What is the location of the Thalamus in the brain?
Functions:
1. Filters and projects cerebral information (relay center) -decides if info is important to go on
2. Visual and auditory information to cortexes - optic and auditory nerves come in and project
3. Regulates consciousness - Damage = coma (lots of drugs impact this area)
4. Influences emotions - many think people with autism have issues with this area
Location in Brain:
Diencephalon
What are the major nuclei of the Thalamus?
Major Nuclei:
1. Anterior group : Part of the limbic system = area where we send info to cerebral cortex, color with emotion
2. Medial group: Emotional output to prefrontal cortex; awareness of emotions = projects sensory to frontal lobe
3. Ventral group: Projects somatic sensory info to somatosensory cortex; relays iinfo from cerebellum and basal nuclei to motor complex = localize where sensory is coming from, develop this as you grow
4. Lateral group: integration of sensory info and infuence of emotional state (see car = friend, relation)
5. Posterior group: two primary senses - visual and auditory
5.1. Lateral geniculate nucleus: projects visual info to the visual cortex
5.2. Medial geniculate nucleus: projects auditory info to auditory cortex
What are the three structures that make up the Diencephalon?
- Epithalamus
- Thalamus
- Hypothalamus
What is the function of the Hypothalamus?
What part of the brain is the Hypothalamus in?
“one ring” - to control them all… head quarters of Autonomic NS
Neurosecretory coordination - makes decision and send out hormones, endocrine and neural system
What does the Hypothalamus respond to?
- Neural stimuli : can change rate of action potentials
- Hormones : tropic hormones, cause other hormone systems to do their job
- Blood/CSF chemical stimuli : direct response to chemical stimulation
What are the major functions of the hypothalamus?
- Autonomic coordination (HR, BP) : viceral activity
- Neurosecretory functions (w/pituitary)
- Physiological drives (hunger, thirst)
- Memory (w/ limbic system)
- Regulation of body temperature
- Control of circadian rhythms : sleep rhythms
- Emotional behavior and sexual response