Unit 10

Question 1

Describe the organization of the mammalian nervous system

Answer 1

The nervous system is divided anatomically into the central nervous system (CNS) and peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, whereas the PNS includes cranial nerves that arise from the brain and spinal nerves that arise from the spinal cord. (Course notes: Nervous system overview, see figure on page)

Question 2

dentify components of the central nervous system

Answer 2

The nervous system is composed of the brain and spinal cord. The brain is composed of neurons and support cells (ex. Microglia, oligodendrocytes)

Question 3

Describe the organization of the brain and identify its embryological development and origins

Answer 3

The brain is developed from the ectoderm, one of the three germ cell layers in the embryo. A groove appears in the ectoderm that deepens and fuses together to form a neural tube. The part of the ectoderm where the fusion occurs becomes a separate structure call the neural crest. Eventually the neural tube becomes the CNS and the neural crest forms the PNS. During the fourth week after conception, the anterior end of the neural tube has three distinct swellings for the forebrain, midbrain and hindbrain. During the fifth week, the forebrain divides into two regions, the midbrain remains unchanged and the hindbrain divides into two regions

Question 4

telencephalon

Answer 4

A division of the forebrain (prosencephalon), develops into the cerebral hemispheres and lateral ventricles

Question 5

diencephalon

Answer 5

A division of the forebrain, develops into the thalamus and hypothalamus and third ventricle

Question 6

mesencephalon

Answer 6

Develops from the midbrain, and remains as the midbrain and aqueduct

Question 7

metencephalon

Answer 7

A division of the hindbrain (rhombencephalon), develops into the pons, cerebellum and upper portion of fourth ventricle

Question 8

mylencephalon

Answer 8

A division of the hindbrain, develops into the medulla oblongata and lower portion of fourth ventricle

Question 9

Identify the ventricles of the brain

Answer 9

The ventricles are fluid-filled cavities formed from the inner cavity of the neural tube. Two lateral ventricles exist, one in each hemisphere, as well as a midline third ventricle and a fourth ventricle in the hindbrain

Question 10

Describe the route of CSF circulation in the mammalian brain

Answer 10

The ventricles and central canal of the spinal cord are connected. The lateral ventricles are found deep to the cerebral hemispheres and join caudally and on the midline to the third ventricle at the level of the diencephalon. At the level of the midbrain, the ventricle narrows into the aqueduct, which communicates with the fourth ventricle at the level of the pons, cerebellum and medulla. The ventricle system continues into the spinal cord as the central canal. CSF escapes the ventricles through small openings called foramen into the subarachnoid space.

Question 11

Describe the function and composition of CSF

Answer 11

Cerebral spinal fluid (CSF) is produced by specialized tissue found in each of the ventricles called the choroid plexuses. The CSF provides nourishment and provides protection as a shock absorber.

Question 12

Identify the layers of the meninges

Answer 12

The brain and spinal cord is encased in three connective tissue layers collectively called the meninges. The outer layer is the dura mater. It is a tough connective tissue layer. Underneath the dura is the arachnoid mater, which is a delicate membrane. The innermost layer is the pia mater, which is delicate and in direct contact with the brain.

Question 13

cerebrum

Answer 13

The structure formed from the telencephalon. It is the largest portion of the brain and is responsible for higher order mental functions.

Question 14

sulci

Answer 14

The depressed grooves of the convolutions of the cerebrum

Question 15

gyri

Answer 15

The elevated folds of the convolutions of the cerebrum

Question 16

nuclei

Answer 16

A group of neuron cell bodies, often found within the white matter (form distinct gray matter regions)

Question 17

gray matter

Answer 17

Makes of the surface of the cerebrum; contains cell bodies

Question 18

white matter

Answer 18

Found deeper in the cerebrum and consists of myelinated axons

Question 19

cerebral hemispheres

Answer 19

The cerebral cortex is divided into a right and left hemisphere that communicate with one another via the corpus callosum.

Question 20

longitudinal fissure

Answer 20

Divides the left and right hemispheres

Question 21

central sulcus

Answer 21

A deep fissure/sulci that divides the frontal lobe from the parietal lobe

Question 22

precentral gyrus

Answer 22

An area involved in motor control located just in front of the central sulcus

Question 23

postcentral gyrus

Answer 23

An area located just behind the central sulcus that contains the somatosensory cortex

Question 24

frontal lobe

Answer 24

Is the anterior portion of each cerebral hemisphere until the central sulcus. It is responsible for voluntary motor control of skeletal muscle, personality, higher intellectual processes and verbal communication.

Question 25

temporal lobe

Answer 25

Is located below the lateral sulcus. It is responsible for interpretation of auditory sensations and memory.

Question 26

occipital lobe

Answer 26

Is located at the back of the brain. It is responsible for intergration of movements in focusing the eye, correlation of visual images with previous visual and other sensory stimuli, and conscious perception of vision.

Question 27

parietal lobe

Answer 27

Is the area behind the central sulcus. It is responsible for somatesthetic interpretation, understanding speech and formulating words, and interpretation of textures and shapes.

Question 28

Describe the basal nuclei and indicate its function

Answer 28

The basal nuclei are a group of nuclei (gray matter) located deep within the white matter of the cerebrum. They are also referred to as the basal ganglia. The basal nuclei are important for the control of voluntary movement.

Question 29

Discuss the limbic system in regards to emotions, memory and olfaction

Answer 29

The limbic system is a group of forebrain nuclei and fiber tracts including the cingulated gyrus, the amygdala, the hippocampus and the septal nuclei. The cingluate gyrus and amygdala are involved in emotion. The hippocampus has been strongly implicated in memory processes and the amygdala is also involved in memory. The limbic system is also involved in the central processing of olfactory information.

Question 30

Identify the basal nuclei and limbic system anatomically

Answer 30

The basal nuclei include the corpus striatum, which is divided into the caudate nucleus, the putamen and the globus pallidus. It also includes the subthalamic nucleus of the diencephalon and the substantia nigra of the midbrain. (See figure 8.12, 13th ed.) The limbic system includes the cingulated gyrus, amygdala, hippocampus and septal nuclei. (See figure 8.15, 13th ed.)

Question 31

thalamus

Answer 31

The thalamus is a region of the diencephalon, accounting for 4/5 of it.

Question 32

hypothalamus

Answer 32

The hypothalamus is a small region of the diencephalon lying below the thalamus.

Question 33

pituitary

Answer 33

The pituitary gland is located immediately inferior to the hypothalamus.

Question 34

Briefly describe the function of the thalamus

Answer 34

The thalamus acts primarily as a relay centre through which all sensory information (except smell) passes on the way to the cerebrum. It is also a key part of the accessory motor system along with the basal nuclei.

Question 35

Describe, in detail, the functions of the hypothalamus

Answer 35

This region contains neural centers for hunger and thirst, the regulation of body temperature, and hormone secretion from the pituitary. The hypothalamus also contributes to the regulation of sleep, wakefulness, sexual arousal and performance, and such emotions are anger, fear, pain and pleasure. Body temperature is controlled through its ability to regulate the autonomic nervous system. Pituitary gland secretions are controlled neuronal stimulation of the posterior pituitary or release of hormones from the hypothalamus to the anterior pituitary. The suprachiasmatic nuclei (SCN) are responsible for the control of circadian rhythms (sleep and wakefulness).

Question 36

Identify the mesencephalon and give its functions

Answer 36

The mesencephalon (or midbrain) is located between the diencephalon and pons. It forms the upper part of the brain stem and contains the red nucleus and the substantia nigra, both involved in motor function. It is also involved in visual reflexes.

Question 37

Identify the pons and cerebellum and discuss their functions

Answer 37

The pons and cerebellum are both regions of the metencephalon. The pons is anterior to the cerebellum and can be seen as a rounded bulge on the underside of the brain. Its name is derived from the Latin for ‘bridge’ as it connects, or bridges, descending pathways from the cerebral cortex to the cerebellar cortex and medulla, and ascending tracts from the medulla to thalamus. The cerebellum is located posteriorly. The cerebellum is needed for motor learning and for coordinating the movement of different joints during movement, as well as the proper timing and force required for limb movements

Question 38

Discuss the medulla oblongata and indicate its vital functions that contribute to homeostasis

Answer 38

The medulla oblongata is derived from the myelencephalon. The medulla is a conduit for ascending and descending nerve fiber tracts that connect the spinal cord to the rest of the brain. The medulla contains the ‘vital centers’, which are important for autonomic control of the heart and peripheral blood vessels, respiratory rate and depth and sneezing (along with centers in the pons), swallowing, coughing and vomiting reflexes.

Question 39

Discuss the reticular activating system

Answer 39

The reticular activating system (RAS) is an ascending arousal system. The RAS can filter out sensory information during sleep, but trigger consciousness when asleep or alertness if drowsy.

Question 40

Differentiate between the spinal column and spinal cord

Answer 40

The spinal cord is a continuation of the medulla. It is protected by the bony spinal column

Question 41

Identify the cervical, thoracic, lumbar, sacral and coccygeal levels on the vertebral column and spinal cord

Answer 41

Cervical: Seven vertebrae located in the neck region, eight nerves

Thoracic: Twelve vertebrae located below the cervical spine through the thoracic cavity, twelve nerves

Lumbar: Five vertebrae located below the thoracic spine in the lower region of the back; the spinal cord terminates at the level of the second lumbar vertebrae and is termed the conus medullaris, five nerves

Sacral: Five fused vertebrae, located in the pelvic region, five nerves

Coccygeal: Four fused rudimentary vertebrae, one nerve

Question 42

Discuss the cauda equina and conus medullaris and its impact to medicine

Answer 42

Cauda equina: The cauda equina is a bundle of spinal nerves and spinal nerve roots, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which originate in the conus medullaris of the spinal cord.

Conus medullaris: Due to differences in growth rate between the spinal cord and vertebral column, the spinal cord terminates at the level of the second lumbar vertebrae and is termed the conus medullaris.

Question 43

Discuss the anatomical arrangement of grey and white matter, dorsal and ventral roots, dorsal root ganglia, central canal

Answer 43

In the spinal cord, the gray matter is located centrally and it is surrounded by white matter. The central gray matter is shaped like an H with two dorsal horns (posterior) and two ventral horns (anterior). Afferent nerves that enter the spinal cord branch into the dorsal root, whereas efferent fibers that leave the spinal cord leave by the ventral root. The ventral and dorsal roots combine before leaving the vertebral column forming a peripheral spinal nerve. The dorsal root ganglion is an enlargement of the dorsal root, and contains the cell bodies of sensory neurons. The cavity of the spinal column is known as the central canal and is filled with CSF.

Question 44

Identify the major tracts of the spinal cord and give their functions

Answer 44

Spinocerebellar: An ascending tract, starting in the spinal cord and terminating in the cerebellum. It conducts sensory impulses to the cerebellum and is necessary for coordinated muscle contractions.

Spinothalamic: An ascending tract, starting in the spinal cord and terminating in the thalamus, then cerebral cortex. The anterior tract conducts sensory impulses for crude touch and pressure. The posterior tract conducts pain and temperature impulses.

Corticospinal: A descending tract, originating in the cerebral cortex. The corticospinal tracts are primarily concerned with the control of fine movements that require dexterity.

Rubospinal: An extrapyrdaminal-descending tract, originating in the red nucleus of the midbrain. This tract influence motor activity via information from the cerebellum.

Reticulospinal: An extrapyramidal-descending tract, originating in the reticular formation (medulla and pons). This tract influence motor activity via information from the cerebellum.

Vestibulospinal: An extrapyamidal-descending tract, originating in the vestibular nuclei (medulla oblongata). This tract influence motor activity via information from the cerebellum.

Question 45

Differentiate between an upper and lower motor neuron

Answer 45

Upper motor neurons are somatic motor neurons with cell bodies in the brain stem and spinal cord and axons that travel within nerves to stimulate skeletal muscle contraction. Upper motor neurons are interneurons in the brain that contribute axons to descending motors tracts and influence lower motor neurons.

Question 46

Describe how the dorsal and ventral roots combine to make a spinal nerve

Answer 46

Each spinal nerve is a mixed nerve composed of sensory and motor fibers. These fibers are packaged together in the nerve, but they separate near the attachment of the nerve to the spinal cord. This produces two “roots” of each nerve. Dorsal = sensory; ventral = motor

Question 47

Identify the name and function of the cranial nerves

Answer 47

I Olfactory: sensory nerve, olfaction

II Optic: sensory nerve, vision

III Oculomotor: mixed nerve, innervation to muscles that regulate the amount of light entering the eye and that focus the lens, proprioception from muscles innervated with motor fibers

IV Trochlear: mixed nerve, motor impulses to superior oblique muscle of eyeball and proprioception from

V Trigeminal: mixed nerve, sensory impulses from facial region, proprioception from muscle of mastication, and motor impulses to muscle of mastication an muscle that tenses the tympanum

VI Abducens: mixed nerve, motor impulses to lateral rectus muscle of eyeball and proprioception from

VII Facial: mixed nerve, motor impulses to muscles of facial expression, secretion of tears, sensory impulses from taste buds, and proprioception from muscle of facial expression

VIII Vestibulocochlear: sensory nerve, sensory impulses associated with equilibrium and hearing

IX Glossopharyngeal: mixed nerve, motor impulses to pharynx used in swallowing and proprioception from, sensory impulses from pharynx, middle-ear cavity, carotid sinus and taste buds, salivation from parotid salivary gland

X Vagus: mixed nerve, controlled of pharynx and larynx, proprioception from visceral muscles, sensory impulses from taste buds and general visceral sensations, regulation of many visceral functions

XI Accessory: mixed nerve, laryngeal movement, motor impulses to muscle in movement of head, neck and shoulders, proprioception from muscles that move neck, head and shoulders

XII Hypoglossal: mixed nerve, motor impulses to muscle of tongue and infrahyoid muscles and proprioception from muscles of tongue

Question 48

Define a reflex arc and identify its components

Answer 48

A reflex is defined as an involuntary response to a stimulus. A reflex arc must have at minimum: a sensory receptor to detect stimulus, a sensory neuron to transmit to spinal cord, a motor neuron to transmit involuntary impulses to an effector and an effector organ which will bring about the response.

Question 49

ipsilateral

Answer 49

on the same side

Question 50

contralateral

Answer 50

taking place or originating in the corresponding part on the opposite side of the body

Question 51

monosynaptic

Answer 51

A type of reflex arc that is compromised of two neurons with one synapse separating the afferent and efferent arms of the reflex

Question 52

polysynaptic

Answer 52

A type of reflex arc that involves multiple synaptic connections

Question 53

afferent

Answer 53

conveying or transmitting inward, towards a center; afferent neurons conduct impulses towards the CNS

Question 54

efferent

Answer 54

conveying or transmitting something away from a central location; efferent neurons conduct impulses away from the CNS

Question 55

interneuron

Answer 55

neurons within the CNS that do not extend into the peripheral nervous system; they are interposed between sensory and motor neurons

Question 56

sensory receptor

Answer 56

a receptor, that when activated sends a signal via a sensory neuron

Question 57

knee jerk reflex

Answer 57

The knee jerk reflex that is elicited when you strike the patellar tendon below the knee and induce contraction of the quadriceps muscle and a resultant kick. This reflex is crucial for maintaining normal posture during standing, movement and locomotion. The sensory receptor is the muscle spindle apparatus, which detects stretch. The effector in this example is skeletal muscle. The knee jerk reflex is localized to one side of the body and is termed ipsilateral (or same side) reflex

Question 58

withdrawal reflex

Answer 58

More complex reflex arcs of the body include the flexor reflex, which occurs in response to painful stimuli in limbs. Grabbing a hot pan from the oven leads to a painful stimuli that is sensed by naked dendrites of afferent neurons. The afferent signal is sent to the spinal cord via the dorsal root. Once the afferent neuron reaches the grey matter of the spinal cord it synapses on an interneuron. This interneuron integrates the sensory information and synapses on multiple efferent neurons that leave the spinal cord via the ventral roots. One efferent signal stimulates flexor muscles and the other inhibits antagonistic extensor muscles that allow for quick and efficient withdrawal of the limb is a manner to minimize further thermal damage.

Question 59

cross-extensor reflex

Answer 59

A more complex withdrawal reflex occurs when you stand on a sharp object like a tack. The painful stimuli is synapses on an interneuron (thus polysynaptic reflex arc) and sends out efferent signals to contract flexor and reflex extensor leg muscle to mediate withdrawal from the penetrating trauma. However, withdrawal from an injured limb when standing will lead to loss of balance further damage to the mammal by falling. Thus a crossed-extensor reflex arc also crosses the midline of the body to mediate contraction of extensor muscles on the opposite limb to support the body’s weight as the injured foot is lifted off the tack.

Question 60

Identify the peripheral nervous system

Answer 60

The peripheral nervous system consists of nerves that connect the CNS to all sensory receptors and effectors of the body.

Question 61

somatic

Answer 61

a motor neuron in the spinal cord that innvervates skeletal muscle

Question 62

autonomic

Answer 62

a division of the nervous system that involves control of smooth muscle, cardiac muscle and glands; it is subdivided into the sympathetic and parasympathetic nervous system

Question 63

preganglionic

Answer 63

autonomic motor control involves two neurons; the preganglionic neuron is the first neuron and synapses with the autonomic ganglion

Question 64

postganglionic

Answer 64

autonomic motor control involves two neurons; the postganglionic neuron is the second neuron and synapses with the target tissue

Question 65

ganglion

Answer 65

a collection of cell bodies outside the CNS

Question 66

Describe the anatomical arrangement of efferent neurons in the autonomic nervous system

Answer 66

The efferent neurons of the ANS involve a preganglionic neuron with its cell body located in the CNS projecting to a ganglion. Here the preganglionic neuron synapses with a postganglionic neuron. This postganglionic neuron is then able to synapse with the target tissue.

Question 67

Indicate the anatomical locations of ganglia in the mammalian body

Answer 67

Autonomic ganglia are located in the head, neck and abdomen as well chains of autonomic ganglia also parallel the right and left sides of the spinal cord. The location of autonomic ganglia helps to distinguish the sympathetic and parasympathetic nervous systems

Question 68

Discuss the differences in the sympathetic vs parasympathetic nervous system in regards to: function, location of ganglia, neurotransmitters employed at chemical synapses, morphology and location of pre-ganglionic and post-ganglionic fibers

Answer 68

• chart *

Question 69

Indicate the anatomical locations of ganglia in the mammalian body

Answer 69

Autonomic ganglia are located in the head, neck and abdomen as well chains of autonomic ganglia also parallel the right and left sides of the spinal cord. The location of autonomic ganglia helps to distinguish the sympathetic and parasympathetic nervous systems.

Question 70

Discuss the sympathetic nervous system and its contribution to homeostasis

Answer 70

Mass activation of the sympathetic nervous system prepares the body for intense physical activity in emegencies; heart rate increases, blood glucose rises, and blood is diverted to skeletal muscles. Sympathetic neurons display tonic activity. As a result, sympatheic nerves tonically regulate the heart, blood vessels and other organs

Question 71

Describe the sympathetic chain and collateral ganglia of the sympathetic nervous system

Answer 71

Many preganglionic fibers that exit the spinal cord below the diaphragm pass through the synaptic chain (of ganglia) without synapsing. These preganglionic fibers form the splanchnic nerve. Preganglionic fibers in the splanchnic nerves synapse in collateral, or prevertebral ganglia. These include the celiac, superior mesenteric, and inferior mesenteric ganglia. Postganglionic fibers that arise from the collateral ganglia innervate organs of the digestive, urinary, and reproductive systems.

Question 72

Discuss the function of the adrenal gland in regards to sympathetic responses

Answer 72

The adrenal medulla (inner region of the adrenal gland) can be likened to a modified sympathetic ganglion. Like a sympathetic ganglion, the cells of the adrenal medulla are innervated by preganglionic sympathetic fibers. The adrenal medulla secretes epinephrine into the blood stream in response to stimulation.

Question 73

Describe the function of the vagus nerve in providing parasympathetic stimulation to viscera

Answer 73

The vagus nerve provides the major parasympathetic innervation in the body. The fibers are quite long are provide parasympathetic innervation to the heart, lungs, esophagus, stomach, pancreas, liver, small intestine, and the upper half of the large intestine.

Question 74

Discuss the responses of various viscera to sympathetic and parasympathetic stimulation

Answer 74

• chart*

Question 75

Identify receptors that provide adrenergic and cholinergic responses

Answer 75

Adrenergic responses: Adrenergic stimulation can have both excitatory and inhibitory responses. Two major classes of adrenergic receptor exist, alpha and beta-adrenergic receptors. All adrenergic receptors act via G-proteins. All subtypes of beta-receptors produce their effects by stimulating the production of cyclic AMP within the target cells. The response of a target cell when norepinephrine binds to the α1 receptors is mediated by a different second-messenger system—a rise in the cytoplasmic concentration of Ca2+. There are certain generalities about the actions of adrenergic receptors. The stimulation of α1 adrenergic receptors consistently causes contraction of smooth muscles. We can thus state that the vasoconstrictor effect of sympathetic nerves always results from the activation of alpha-adrenergic receptors. Stimulation of beta-adrenergic receptors promotes the relaxation of smooth muscles (in the digestive tract, bronchioles, and uterus, for example) but increases the force of contraction of cardiac muscle and promotes an increase in heart rate.

Cholinergic responses: All somatic motor neurons, all preganglionic neurons (sympathetic and parasympathetic), and most postganglionic parasympathetic neurons are cholinergic—they release acetylcholine (ACh) as a neurotransmitter. The effects of ACh released by somatic motor neurons, and by preganglionic autonomic neurons, are always excitatory. The effects of ACh released by postganglionic parasympathetic axons are usually excitatory, but in some cases they are inhibitory. There are two main types of cholinergic receptors—nicotinic and muscarinic. There are five different subtypes of muscarinic receptors (M1 through M5). Some of these cause contraction of smooth muscles and secretion of glands, while others cause the inhibition that results in a slowing of the heart rate. Some (e.g. M3) can cause an excitation (stimulating release of EDRF), which ultimately turns into an inhibitory effect (EDRF causes relaxation of arteriolar smooth muscle).