Lecture 14, The CNS and Sub-Cortical Areas Flashcards
Neuron vs Nerve
a neuron = a single nervous cell
a nerve = a group of axons plus connective tissue wrappings and blood vessels
- endoneurium: connective tissue covering around individual axon
- perineurium: connective tissue covering around an individual fascicle
- epineurium: connective tissue covering around the entire nerve (contains blood vessels to bring nutrients and support metabolic activity)
- nerves are only found in the PNS
- in the CNS, groups of axons that are travelling together are called pathways of tracts
- if the tract links two halves of the brain, it is called a commissure
The Central Nervous System
the CNS = the brain and spinal cord
the brain has three major divisions:
1. forebrain (cerebrum and diencephalon)
2. midbrain
3. hindbrain (pons, medulla oblongata, cerebellum)
the spinal cord emerges from the brain, and extends down the ~L1-L2
the brain also has fluid-contained cavities, known as cerebral ventricles
Division of the Brain
the outer layer of the cerebrum is called the cerebral cortex, and can be divided into lobes:
- frontal lobe: voluntary movement, executive functions, consciousness, personality
- parietal lobes - sensory perception and integration, language processing
- occipital lobes - visual perception and processing, facial/object recognition
- temporal lobes - auditory perception and processing, memory retrieval
-> the cerebrum has two hemispheres separated by a longitudinal fissure
-> the cerebral cortex consists on an outer layer of grey matter, and underneath it likes an inner layer of white matter
-> subcortical nuclei are cell clusters that reside deep to the cortex
The Cerebral Cortex - sensory areas
neurons of common function are localized together in the areas of the cortex
- functions of the cortex can be mapped for specific areas
sensory area: receive sensory information, generate sensations
The Cerebral Cortex - motor areas
motor areas: initiate and direct voluntary movement by acting on brainstem and spinal cord
The Cerebral Cortex - primary sensory (somatosensory) cortex
- located posterior to the central sulcus in the parietal lobe
- receives input from sensory receptors in the skin and muscles
- the right hemisphere receives information from the left side of the body and the left hemisphere receives information from the right side of the body
The Cerebral Cortex - somatosensory associated area
somatosensory associated area: located posterior to the primary sensory cortex, this areas aids in the interpretation of touch, pain and temperature
The Cerebral Cortex - primary motor cortex
- located anterior to the central sulcus on the frontal love (In the precentral gyrus)
- initiates voluntary movement from triangular shaped neurons (pyramidal cells - which are the largest cells in the CNS)
- axons on these neurons project to the spinal cord, where they send signals to motor neurons
- similar to the primary sensory cortex, each hemisphere of the primary motor cortex control the contralateral side of the body
The Cerebral Cortex - premotor cortex
- located anterior to the primary motor cortex
- stores information regarding learned motor skills (i.e., playing a musical instrument, writing, typing)
- sends this information to the primary motor cortex
the amount of sensory or motor cortex devoted to each of part of the body determines how sensitive it is, how we much motor control we have over that region of the body - homunculus
Homunculus
-> more sensitive regions of the body (ex. mouth, hands), have a larger region of sensory cortex devoted to it
-> parts of the body that have greater motor control (ex. hands), have a larger region of motor cortex devoted to it
The Cerebral Cortex - primary auditory cortex
- located in the superior portion of the temporal lobe, this area receives information from cochlear receptors in the inner ear that allows us to hear
- both left and right hemispheres receive information from both ears
The Cerebral Cortex - primary visual area
- located on the posterior tip of the occipital lobe (is the largest of the cortical sensory areas)
- receives half of the information from the retinas of both eyes (the left half of the visual cortex represents information from the left half of each retina, and vice versa with the right
The Cerebral Cortex - visual association area
- surrounds the primary visual cortex and forms many connections with it
- the area stores information that allows us to recognize visual information (ex. facial or object recognition)
The Cerebral Cortex - olfactory area
- located on the medial/anterior portions of the temporal lobes, the orbitofrontal cortex, and part of the limbic system
- these areas receive information from small receptors in the nasal cavities
- information is sent through the olfactory bulb to these cortical areas
The Cerebral Cortex - prefrontal cortex
- receives information from association areas and analyzes/interprets it
- plays a role in the formation of feelings in response to received information
- is also involved in personality, intellect, complex learning abilities (cognition), and memory (these traits develop over time, largely depending on experience)
- is linked to the emotional and learning system of he brain known as the Limbic System
Basal Nuclei
the basal are a subcortical structure
- play a role in planning voluntary movement, by sending signals to the primary motor cortex via the thalamus
- the basal nuclei play a key role in the execution of voluntary movement (inhibits unnecessary movement and antagonist muscles)
main functions:
- subconscious control of skeletal muscle tone
- coordination of learned movement patterns (rhythms)
- generation of body position
The Limbic System
the limbic system is a functional system, rather than a set of anatomical structure; includes:
- nuclei in different part of brain (frontal and temporal lobes) and the tracts that connect them
- hippocampus and amygdala
- thalamus and hypothalamus
- olfactory bulbs (help contribute to sensation of smell)
Main Functions of The Limbic System
main functions of the limbic system relate to emotional control and regulation:
1. establishes emotional states
2. links conscious intellectual functions of cerebral cortex and autonomic functions
3. creates emotional drives
4. facilitates memory storage and retrieval
secondary functions include learning and some endocrine functions
Thalamus
the thalamus is a cluster of nuclei that sends and receives information to/from the cortex
- also known as the “Gate to the Cortex”
- primary functions is to receive sensory information and relay this to the appropriate area in the cortex
- also receives information from the basal nuclei, and relays it to the primary motor cortex
Hypothalamus
the hypothalamus lies below the thalamus, on the undersurface of the brain
- forms the command center for neural and endocrine coordination
- is an important control area for homeostatic regulation of the internal environment
◦ cardiovascular and vasomotor control, regulation
of temperature, etc.
◦ control of circadian rhythms via the pineal gland,
which is responsible for melatonin release
the hypothalamus is connected to the pituitary gland, which is an important endocrine structure
-> gland is just a tissue that secretes something
Grey and White Matter
grey matter is composed of the cell bodies of neurons
white matter is composed on the tracts of myelinated axons
- white matter is deep to the grey matter in the brain
- but contains subcortical structures that are composed of grey matter
- white matter is superficial to the grey matter in the spinal cord
Meninges
between the soft neural tissues (brain and spinal cord) and the bones that surround them (skull and vertebrae) are three layers of membranous coverings
the meninges:
* dura mater - the outermost layer that is closest to the skull and vertebrae (dense collagen network)
- arachnoid mater - the middle layer that lies between the dura and pia maters (not as dense, made of collagen and elastic fibers)
- pia mater - the deepest layer that is closest to the brain and spinal cord (very thin; collagen and elastic fibers) -> closely associated with the brain
the subarachnoid space is between the arachnoid and pia maters, and is filled with cerebrospinal fluid
* provides cushioning for the CNS
-> arachnoid and subarachnoid space can be sponge-like
Meninges (2)
the pia mater is very closely associated with the brain - follows the ridges and bumps of the cortex
- is a very thin, transparent layer of connective tissue that adheres to the surface of the brain
- contains blood vessels that supply oxygen/nutrients to the brain
the arachnoid mater looks like a spider’s web “arachnoid”
the dura mater is a thick connective tissue structure, and exists in a double-layer around the brain
- veins can pass between the layers and in some areas, such as the superior sagittal sinus (shown in picture)
Meninges Also Cover the Spinal Cord
the meninges around the brain are continous with the meninges around the spinal cord
- pia mater also closely follows the grooves of the spinal cord
the epineurium is fused with the dura mater
epidural space is the space between the dura mater and the vertebral wall
- contains CSF
Meningeal Extensions
the meninges around the brain also form extensions that divide parts of the brain
- falx cerebri - separates the two hemispheres of the cerebrum
- falx cerebelli - separates the two hemispheres of the cerebellum
- tentorium cerebelli - separates the cerebrum from the cerebellum
Meningitis
meningitis: inflammation of the meninges
- is a serious life threatening condition
- bacterial or viral meningitis can spread to the CNS
- if the brain becomes inflammed this is called encephalitis
- meningitis can cause increased intracranial pressure, seizures and loss of consciousness
meningitis can be diagnosed by examining a sample of CSF takes from the subarachnoid space in the spinal column
Cerebrospinal Fluid (CSF)
CSF is secreted by ependymal cells in the choroid plexus, a structure in the ventricles of the brain
- is contained in the ventricles, sub-arachnoid space, and central canal (epidural space) in the spinal cord
- the ventricles and the central canal are all connected
- functions to supply oxygen and nutrients and remove waste products, as well as cushion the brain (chemical and mechanical protection)
the total volume of CSF in the body at a given time is 150 mL
the body produces ~500 mL of CSF per day
CSF is resorbed in the subarachnoid space, and leaves the CNS via the vein in the superior sagittal sinus
