Chapter 12 - Central Nervous System

Regions of the Brain:

1. Cerebral hemispheres

2. Diencephalon (thalamus, hypothalamus, epithalamus)

3. Brain stem

4. Cerebellum

The cerebral hemispheres and cerebellum have:

1. outer "bark" or cortex of gray matter (neuron cell bodies)

2. a middle region of white matter (myelinated)

3. an inner gray matter core of brain nuclei.

1. Describe the ventricles of the brain.

Continuous with each other and with the central canal of the spinal cord. Filled with CSF and lined by ependymal cells. Paired lateral ventricles (C-shaped) located deep within each cerebral hemisphere. Lateral ventricles connect with the narrow third ventricle in the diencephalon. Third ventricle is continuous with the fourth ventricle which is continuous with the central canal of the spinal cord. Three openings connect the ventricles with the subarachnoid space (a fluid filled space surrounding the brain)

2. Define gyri, sulci, and fissures.

Cerebral Hemispheres: Nearly the entire surface is marked by elevated ridges called gyri (gyrus, singular) which are separated by grooves called sulci (sulcus, singular). The deepest of the grooves are called fissures. Median longitudinal fissure separates the hemispheres, and the transverse fissure separates the hemispheres from the cerebellum.

3. Describe the functional areas of the cerebral cortex.

Three basic regions to each hemisphere: Outer cerebral cortex of gray matter, Internal

cerebral white matter, Basal nuclei.

Cerebral Cortex: Enables us to perceive, communicate, remember, understand, initiate voluntary movements conscious behavior. Composed mainly of neuron cell bodies and unmyelinated fibers. About 40% of the total brain mass. Specific motor and sensory functions are localized in discrete cortical areas called domains. Many higher mental functions, such as memory and language, appear to have overlapping domains.

Three kinds of functional areas:

1. motor areas -control voluntary motor functions

2. sensory areas- conscious awareness of sensation

3. association areas-integrate diverse information for purposeful action.

Each hemisphere is concerned with the sensory and motor functions of the opposite side of the body. No functional area of the cortex acts alone. Conscious behavior involves the entire cortex.

4.  Locate and describe function of 4 motor areas and 4 sensory areas of cerebral

cortex.

Motor Areas:

Cortical areas controlling motor functions lie in the posterior part of the frontal lobes.

1. Primary motor cortex: allows for conscious control of skeletal muscle movement. Entire body is represented spatially in this area.

2. Premotor cortex: controls learned motor skills of a repetitious nature. Memory bank for skilled motor activities.

3. Broca's area: special motor speech area that directs the muscles of the tongue, throat, and lips.

4. Frontal eye field: controls the voluntary movement of the eyes.

Sensory Areas:

Concerned with conscious awareness of sensation.

1. Primary somatosensory cortex: receives information from sensory receptors in skin and muscles.

2. Somatosensory association area: integrate and analyze different somatic sensory inputs into a comprehensive evaluation of what is being felt relative to size, texture, and

relationship of its parts.

3. Visual areas: receives information that originates in the eyes; interprets these visual

stimuli in light of past visual experiences.

4. Auditory areas: Permits the perception of the sound stimulus.

 

 

5. Contrast left and right hemisphere functions.

There is division of labor, and each hemisphere has unique abilities not shared by its partner "split brain concept." In most people, the left hemisphere has greater control over language abilities, math abilities, and logic. The right hemisphere is more involved in visual-spatial skills, intuition, motion, and appreciation of art and music. Most individuals with left cerebral dominance are right-handed and vice versa.

6.  Identify and describe functions of basal nuclei and the diencephalon components (thalamus, hypothalamus, and epithalamus).

Cerebral White Matter

Provides for communication between cerebral areas and between the cerebral cortex and

lower CNS centers.Consists largely of myelinated fibers bundled into large tract.

Basal Nuclei: Deep within the cerebral white matter of each hemisphere is a group of

subcortical nuclei called basal nuclei or basal ganglia. Influence muscle movements directed by the primary motor cortex. Also may play a role in cognition. Thought to be particularly important in initiating and monitoring movements, especially those that are relatively slow and sustained (swinging arms).

THE DIENCEPHALON:

THALAMUS - has many different nuclei, each of which has a functional specialty.

All sensory inputs ascending to the cerebral cortex are funneled through the thalamic nuclei. Sorting out and information editing process occurs. The thalamus plays a role in mediating: sensation, motor activities, cortical arousal, memory. Gateway to the cerebral cortex

HYPOTHALAMUS - Named for its position below the thalamus. Caps the top of the brainstem. The infundibulum is a stalk of the hypothalamic tissue chat connects the pituitary gland to the base of the hypothalamus. Main visceral control center of the body.

Chief homeostatic roles are:

1. Autonomic control center - regulates involuntary nervous system activity. Influence blood pressure, rate and force of heart, contraction, motility of the digestive tract, respiratory rate and depth, eye pupil size.

2. Center for emotional response and behavior - involved in the perception of pain, pleasure, fear, and rage, as well as those involved in biological rhythms and drives.

3. Body temperature regulation - body's thermostat. Monitors the temperature of blood flowing through the hypothalamus and initiates cooling or heat retention mechanisms.

4. Regulation of food intake - regulates feeding behavior.

5. Regulation of water balance and thirst

6. Regulation of sleep-wake cycle

7. Control of endocrine system functioning

EPITHALAMUS - Most dorsal portion of the dienchephalon. Extending from its posterior border and visible externally is the pineal body or gland, which secretes melatonin (hormone). Along with the hypothalamus, involved in regulation of the sleep-wake cycle and some aspects of mood. A CSF-forming structure (choroid plexus) is part of the epithalamus.

7.  Identify and describe functions of the brain stem (midbrain, pens, medulla).

Positioned between the cerebrum and the spinal cord. Centers produce the rigidly

programmed, automatic behaviors necessary for our survival. Provides a pathway for fiber tracts running between higher and lower neural centers.

MIDBRAIN - Located between the diencephalon and the pons.Contain nuclei controlling visual reflex centers that coordinate head and eye movement, and part of the auditory relay from the hearing receptors of the car to the sensory cortex.

PONS - Located between midbrain and medulla. Chiefly composed of conduction tracts.

These fibers course in two directions through the pens. The deep fibers run longitudinally

and complete the superior-inferior pathway between higher brain centers and the spinal cord. Other important nuclei are respiratory centers. they help to maintain the normal rhythm of breathing.

MEDULLA OBLONGATA - Most inferior part of the brain stem. Just above the medulla-spinal cord junction, most of the fibers cross over to the opposite side before continuing their descent into the spinal cord. The consequence of this crossover is that each cerebral hemisphere chiefly controls the voluntary movements of muscles on the opposite side of the body. Nuclei within this area, are involved in mediating responses that maintain equilibrium. Important visceral nuclei found are: cardiac center - adjusts the force and rate of heart contractions, vasomotor center - regulates blood pressure, respiratory center -controls rate and depth of breathing, other centers that regulate activities such as vomiting, hiccuping, swallowing, coughing, and sneezing.

8.  Identify and describe function of cerebellum.

Processes inputs received from the cerebral cortex, various brain stem nuclei, and sensory

receptors. Provides precise timing, and appropriate patterns of skeletal muscle contraction needed for smooth, coordinated movements. Like an automatic pilot. It continually compares the higher brains intention with the body's actual perfomance and sends out messages to initiate the appropriate corrective actions. Helps promote smooth voluntary movements that are precise and economical in terms of muscular effort.

9.  Describe the structure and functions of the limbic system and the reticular activating system.

LIMBIC SYSTEM is spread widely throughout the forebrain. This system is our emotional, or affective (feeling) brain. Extensive connections between the limbic system and lower and higher brain regions allow the system to integrate and respond to a wide variety of environmental stimuli. The hypothalamus is the neural clearinghouse for autonomic and emotional responses. It is the reason why acute stress causes visceral illnesses (ulcers, hypertension, etc). The most severe consequence of severe emotional distress is cardiac arrest. The links with the cerebral cortex help explain why emotion sometimes overrides thoughts and why reason can stop us from inappropriate expression of emotion.

RETICULAR SYSTEM: Extends through brainstem; governs arousal of brain as a whole. Certain fibers maintain cortex in an alert, conscious state (the reticular activating system). The RAS appears to act as a filter for the flood of sensory input. Repetitive, familiar or weak signals are filtered out. Between the RAS and the cerebral cortex, perhaps 99% of all sensory stimuli are disregarded. If not, the sensory overload would be overwhelming.

10. Describe the structure and function of the meninges of the brain (dura mater, arachnoid, pia mater).

The brain is protected by the skull, cushioned by the CSF, protected by the blood-brain barrier, and also by the meninges - 3 connective tissue membranes on the outer surface of the brain and spinal cord.

Dura mater: Toughest of the membranes that surround the brain. In several places the dura mater extends inward to anchor brain to skull and limit excessive movement in the cranium.

Arachnoid mater: Forms a loose brain covering. Beneath the membrane is the subarachnoid space which is filled with CSF and contains the largest blood vessels serving the brain.

Pia mater: Composed of delicate connective tissue. Clings tightly to brain, follows every convolution.

11.  Describe composition and function of cerebrospinal fluid.

Found in an around the brain and spinal cord Forms a liquid cushion and gives buoyancy to the CNS organs. By floating the brain, the CSF effectively reduces brain weight by 97% and prevents the brain from crushing under its own weight. Also protects the brain and spinal cord from blows and other trauma. CSF helps to nourish the brain; watery broth similar in composition to plasma. The choroid plexuses help to cleanse the CSF by removing waste products and other unnecessary solutes. Circulates through ventricles of brain and central canal of spinal cord and in the subarachnoid space of brain and spinal cord.

12.  Describe the blood-brain barrier.

Protective mechanism that helps ensure that the brain's environment remains stable.

Blood-borne substances within the brain's capillaries are separated from the extracellular space and neurons by:

1. continuous endothelium of the capillary wall

2. relatively thick basal lamina surrounding the capillary

3. the bulbous "feet" of the astrocytes that cling to the capillaries.

It is absent in the vomiting center of the brain stein, which monitors the blood for poisonous substances and in the hypothalamus, which regulates water balance, body temperature, and many metabolic activities, where it is essential to allow the hypothalamus to sample the chemical composition of the blood.

13.  Describe structure and function of the spinal cord.

Major reflex center: spinal reflexes are initiated and completed at the spinal cord level.

Pathway for nerve impulses to and from the brain. Spinal cord is protected by bone, CSF, and meninges. 31 pairs of spinal nerves arise from the cord by paired roots and exit the column via the intervertebral foramen to travel to the body regions they serve.The cord has two obvious enlargements (cervical and lumbar) where the nerves serving the upper and lower limbs arise. The lumbar and sacral spinal nerve roots angle sharply down ward and travel inferiorly through the vertebral column for some distance before reaching their foramina. The nerve roots at the inferior end are called the cauda equina (horse's tail). In cross section, gray matter appears in a shape of a butterfly (consists of neuron cell bodies, unmyelinated axons, and dendrites) and white matter is exterior (myelinated axons of tracts).

14.  Describe gray matter of spinal cord.

Gray matter is subdivided into regions called horns (anterior, posterior, and lateral). Anterior horns are largest in the regions serving the limbs - associated with voluntary motor activity. Lateral horns contain autonomic motor neurons that serve visceral organs. Motor fibers leave the cord via the ventral root. Sensory fibers come into the cord via the dorsal root. Sensory neuron cell bodies are located in the dorsal root ganglion. Dorsal and ventral roots fuse to form spinal nerves.

15.  Describe white matter of spinal cord.

Composed of myel;nated fibers that travel up brain and brainstem (sensory), down from brain and brainstem (motor), and across from one side of the cord to the other. White matter is made up of tracts - multineuron pathways that connect brain to body periphery.

Ascending tracts are sensory. Descending tracts are motor.