Block Theory 2

Question 1

What are the functions of the nervous system?

Answer 1

The nervous system controls voluntary and involuntary processes with three processes:

1) Sensory Input: gathers vital sensory information about external and internal environments with sensory nerves that detect input and travel through the body to communicate with other nerve cells.

2) Integration: incorporates simultaneous signals to create a picture of the environment.

3) Motor Output: appropriate response to input is sent by motor output signals through motor nerves that communicate from the brain and spinal cord to the skeletal, smooth, or cardiac muscle, causing them to relax or contract.

Question 2

What are the two subdivisions of the nervous system?

Answer 2

CNS: made of brain and spinal cord (control center)

PNS: composed of all nerves outside the brain and spinal cord (cranial, spinal, autonomic nervous system, and special sense organs)

Question 3

What are the different divisions of the PNS?

Answer 3

Efferent (Motor): relays information from the CNS to target cells

Afferent (Sensory): relays information to the CNS

Question 4

What is the difference between somatic and autonomic signalling?

Answer 4

Somatic: voluntary

Autonomic: involuntary

Question 5

What is the difference between sympathetic and parasympathetic response?

Answer 5

Sympathetic: fight-or-flight

Parasympathetic: rest-and-digest

Question 6

What are neurons?

Answer 6

Neurons are cells that are excitable and can generate and transmit rapid electrical signals to other neurons.

Dendrites: receive signal from other neurons and transfer it to the cell body.

Cell Body (soma): houses nucleus and organelles and functions to transfer electrical signals from the dendrites to the axon body.

Axon: carry signals from cell body to axon terminals where the signals are transferred to other neurons or organs.

Question 7

What are the classifications of neurons?

Answer 7

Neurons are classified based on the number of processes they have.

Pseudounipolar: one cellular process that splits into a dendrite and an axon

Bipolar: have two distinct cellular processes (sight/hearing)

Multipolar: have multiple dendrites and one axon (most common- motor neurons)

Question 8

What are supporting cells?

Answer 8

Supporting cells, known as neuroglia or glia, protect and support neurons, as well as aid in sending signals between neurons to improve communication. They do not generate nerve impulses.

Astrocytes: large star shaped cells in the CNS with numerous processes that communicate with neurons and blood vessels to maintain neural tissue integrity. (most abundant)

Microglia: small glial cells in the CNS that phagocytose pathogens and eliminate waste from other cells. (least common)

Ependymal: cuboidal and line cavities in the CNS for production, circulation, and monitoring of CSF.

Oligiodendrocytes: wrap around axons in the CNS to form myelin sheath with many processes.

Schwaan Cells: form myelin sheath around axons in the PNS

Question 9

What is myelin?

Answer 9

Myelin is a fatty coating around axons that appears white and insulates to increase the speed at which electrical signals travel.

The regions that are unmyelinated are nodes of Ranvier (neurofibril nodes).

Question 10

What is the cerebrum?

Answer 10

The cerebrum makes up the bulk of the brain with telencephalon and diencephalon.

Question 11

Discuss telencephalon.

Answer 11

Telencephalon interprets sensory signals, sends motor signals, and regulates decision making.

Cerebral Hemispheres:the cerebrum has the left and right hemispheres that are separated by the longitudinal fissure.

Cerebral Cortex: the outer layer of the cerebrum that appears a dark grey colour.

Sulci/Gyri: folding in the cerebrum increases surface area and functional capacity of neural tissue. Sulci are fissures and grooves that divide the brain into regions with different functions. Gyri are lumps and bumps that correspond to function. The precentral gyrus (motor cortex) sends motor output signals, while the postcentral gyrus (somatosensory cortex) receives sensory input (touch).

Lobes: have specific functions and are named based after the overlying skull bones.

Grey Matter: has nerve cell bodies, short interneurons, and glial cells in the cerebral cortex/inner brain areas.

White Matter: has bundles of nerve fibres and axons that make up tracts for neural communication.
- Association: communication in 1 hemisphere
- Commissural: communicate between 2 hemispheres (corpus callosum)
- Projection Fibres: communication between brain and spinal cord

Question 12

What is Lissencephaly?

Answer 12

a syndrome characterized by a lack of sulci and gyri that results in limited mental capacity, slow physical development, and life incompatibility after 10.

Question 13

Discuss diencephalon.

Answer 13

Diencephalon is deep to the telencephalon as the central core of the cerebrum, surrounded by the hemispheres.

It is responsible for sensory and motor relay into and out of the brain, as well as control of the autonomic nervous system.

Thalamus: has two bodies responsible for relaying sensory information, except smell, to areas of the brain.

Hypothalamus: connected to pituitary gland to control the release of hormones.

Question 14

What are the areas of the brainstem?

Answer 14

The brainstem connects the brain to the spinal cord and is essential for human functioning and survival with autonomic reflex centers and white matter tracts.

Midbrain: has large white matter tracts that make up the cerebral peduncles and two bumps known as superior/inferior colliculi.

Pons: has fibres connecting to the cerebellum for communication.

Medulla: continuous with the spinal cord

Question 15

What is the cerebellum?

Answer 15

The cerebellum sits under the occipital lobe and functions to coordinate motor activity.

Question 16

Discuss the meninges.

Answer 16

The meninges has 3 connective tissue membranes that protect CNS structures.

Dura Mater: most superficial and tough with a double layer of connective tissue that attaches to the skull. Makes the falx cerebri between hemispheres, tentorium cerebelli between the cerebrum/cerebellum, and the falx cerebelli at the midline of the cerebellum.

Arachnoid Mater: loosely covers the brain, creating the subarachnoid space filled with CSF and blood vessels.

Pia Mater: innermost layer, firmly attached to cerebral cortex.

Question 17

What are ventricles?

Answer 17

Ventricles provide support and protection to the brain with 4 hollow spaces that are continuous with each other and the spinal cord, containing CSF.

Lateral: ‘c’ shaped spaces in hemispheres with a portion in each lobe.

Third: in the middle of the diencephalon, connected to the lateral ventricles with the interventricular foramina.

Fourth: sits between the pons/medulla and the cerebellum, connected to the third ventricle with the cerebral aqueduct. It is continuous with the central canal of the spinal cord and thee subarachnoid space.

Question 18

What is the flow direction of CSF?

Answer 18

lateral ventricles, interventricular foramen, third ventricle, cerebral aqueduct, fourth ventricle, subarachnoid space.

Question 19

Explain the spinal cord.

Answer 19

The spinal cord is located in the vertebral canal and is supported by the vertebral column to facilitate communication between the CNS and PNS through spinal nerves that exit the spinal cord to supply sensory and motor innervations to regions close to the level of exit

Question 20

What is the external topography of the spinal cord?

Answer 20

The spinal cord begins at the foramen magnum and extends to L2 (conus medullaris), then beyond where emerging axons (cauda equina) have thin strands of pia mater (filum terminale) that anchor the spinal cord to the sacrum and coccyx.

Regions of the spinal cord are named the same as the vertebrae, but since shorter, the regions are not located in the same areas.

Question 21

What are the spinal enlargements?

Answer 21

Spinal enlargements occur where the additional nerves exit the spinal cord to supply the limbs. (cervical - upper, lumbar - lower)

Question 22

What are the different levels of spinal injury?

Answer 22

C1-C3: limited movement of head/neck

C3-C4: head, neck, limited shoulder

C5: head, neck, shoulders, elbows, hands

C6-C7: head, neck, shoulders, arm, wrist

C8-T1: head, neck, shoulders, arm, wrist, fingers

T2-T6: impairment of legs

T7-T12: more function of legs

L: move hip and knees

Question 23

What are the meninges of the spinal cord?

Answer 23

Dura Mater: single layer of connective tissue with a fat-filled epidural space on the exterior.

Arachnoid Mater: makes subarachnoid space that is continuous with that of the brain and contains CSF.

Pia Mater: directly attached to spinal cord

Question 24

What is the internal topography of the spinal cord?

Answer 24

The spinal cord has an outer white matter and inner grey matter structure where the appearance is evident due to cell types.

Grey Matter: ventral horn carries motor information, while dorsal horn carries sensory information, and in between is the lateral horn which carries information from the sympathetic nervous system.

White Matter: has tracts of fibres that separate into anterior, lateral, and posterior funiculi.

Question 25

What are cranial nerves?

Answer 25

There are 12 cranial nerves that emerge in pairs from the brain and brainstem that only carry sensory information, only motor information, or carry both sensory and motor information. They are numbered using Roman numerals and can be referred to by number or name.

I (olfactory nerve): sensory - smell
II (optic nerve): sensory – vision
III (oculomotor nerve): motor – movement of the eye
IV (trochlear nerve): motor – movement of the eye
V (trigeminal nerve): sensory – forehead, eye, upper jaw, lower jaw; motor – muscles of mastication
VI (abducens nerve): motor – movement of the eye
VII (facial nerve): sensory - taste for anterior 2/3 of tongue; motor - muscles of facial expression, parasympathetic innervation of tear and salivary glands
VIII (vestibulocochlear nerve): sensory – equilibrium and hearing
IX (glossopharyngal nerve): sensory – innervation of the pharynx, taste from posterior 1/3 of tongue; motor – pharynx muscles, parasympathetic innervation of salivary glands
X (vagus nerve): sensory - innervation of the larynx; motor - pharynx and larynx muscles, parasympathetic innervation of the thoracic and abdominal organs
XI (accessory nerve): motor – trapezius and sternocleidomastoid muscles
XII (hypoglossal nerve): motor – muscles of the tongue

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Question 26

What are the spinal nerves?

Answer 26

Spinal nerves are named as such because they emerge from the spinal cord. There are 31 pairs of spinal nerves that carry information through the PNS. Spinal nerve is formed by the union of the posterior (sensory) and anterior (motor) roots of the spinal cord.

Spinal nerves are identified based on a letter and number. The letter refers to the region of the spinal cord, while the number refers to the level.

In the cervical region, spinal nerves emerge superior to the corresponding vertebrae. Spinal nerve C8 is the exception, emerging between C7 and T1. Below the neck, all spinal nerves emerge inferior to its corresponding vertebra.

Question 27

What are nerve plexuses?

Answer 27

When spinal nerves exit the vertebral column, fibres from the anterior roots come together and re-distribute into new networks of plexus is that innervate muscles of the limb. Each plexus contains fibres from a combination of spinal nerves with functional importance in case of injury, because multiple spinal nerves in plexuses ensure innervation to the muscle. The main spinal nerve plexuses corresponds to the enlargement of the spinal cord. The cervical and brachial plexus is correspond to the cervical enlargement, while the lumbar and sacral plexus is correspond to the lumbosacral enlargement.

Question 28

What is the autonomic nervous system?

Answer 28

The autonomic nervous system is known as the visceral motor system and is responsible for transmitting involuntary signals from the CNS to smooth muscles, cardiac muscles, and glands.

Question 29

What is the organization of the autonomic nervous system?

Answer 29

The autonomic nervous system is a two neuron pathway between the CNS and any target organ.

Preganglionic fibers: has its cell body within the CNS and its axon entering into the PNS and travelling to the autonomic ganglion.

Autonomic ganglion: where the preganglionic and postganglionic neurons meet and communicate in the PNS.

Postganglionic neuron: entirely in the PNS with its cell body in the autonomic ganglion and its axon travelling to the target organ.

Question 30

What are the differences between the sympathetic and parasympathetic nervous systems?

Answer 30

Sympathetic: spinal cord segment T1 to L2 (Thoracolumbar division), fight or flight response, and widely distributed affect to many parts of the body.

Parasympathetic: brainstem and spinal cord segment S2 to S4 (Craniosacral division), rest and digest response, limited distribution to target organs with localized effects.

Question 31

Describe the sympathetic pathway.

Answer 31

1- Sympathetic preganglionic axons leave the lateral horn of the spinal cord with somatic motor axons to form the anterior route.

2- Preganglionic axons passed through the spinal nerve to the sympathetic trunk, a structure lateral to the spinal cord on either side. The sympathetic trunk provides a pathway for the sympathetic fibres to travel through the body both superiorly and inferiorly.

3- Preganglionic neurons synapse with the postganglionic neurons in the ganglia.

4- Postganglionic axons leave the sympathetic trunk to enter the spinal nerve and extend to the effect or tissue/organ at approximately that vertebral level.

Question 32

Describe the parasympathetic pathway.

Answer 32

1- Preganglionic neurons leave the brain or spinal cord at the level of the sacrum.

2- Preganglionic neurons meet postganglionic neurons and ganglia close to viscera.

3- Post ganglionic neurons travel to effector organs (CNIII/VII/IX - head, CNX - thorax to descending colon, S2/3/4 - terminal gut and pelvic viscera)

Question 33

Discuss vision.

Answer 33

Vision requires special visual receptors called photoreceptors located at the back of the eye.

Question 34

What are the accessory structures of the eyeball?

Answer 34

Lacrimal gland: produces tears to keep the cornea and outside surface of the eyeball moist and clean. The tear drainage system is also very important as part of the lacrimal apparatus.

Eyelid: upper eyelid contains the le at or palpebrae superioris muscle and orbicularis oculi muscle to control the opening and closing of the eyelid.

Extrinsic eye muscles: 6 extrinsic eye muscles allow you to move your eyes to increase range of motion.

Extraocular eye muscles: located outside of the eyeball and named based on location.

Question 35

What are the general features of the eye?

Answer 35

The eye is a globe structure with the majority of it situated within the skull. It is a complex organ with many features and layers.

Question 36

What are the cavities of the eye?

Answer 36

There are two fluid filled cavities that are delineated by the lens.

Anterior cavity: composed of the anterior and posterior chambers that are filled with aqueous humour (watery)

Lens: separates the interior cavity and the posterior cavity.

Posterior cavity: compartment filled with vitreous humour (gelatinous)

Question 37

What are the layers of the eye?

Answer 37

The eye is composed of three layers, or tunics.

Deep layer - sensory (retina): The innermost layer of the eye
-Neural layer: has photo receptors that are light sensitive cells which send signals through smaller nerves to the axons of ganglion cells to form CNII
-Optic disc: area were smaller nerve cell axons converge. It is the location we see you when we look into the eye.
-Optic nerve: CN II
-Macula: central area of the retina with a depression, the fovea, where fine detail division occurs.

Middle layer - vascular: middle layer of the eye.
-Chorid: Contains blood vessels that supply the eye with oxygen and nourishment
-Ciliary Body: produces aqueous humour and contains the ciliary muscles which control the shape of the lens
-Iris: contains the sphincter and dilator muscles that control the narrowing and widening of the people while also containing pigment that gives the eye its color.

Outer layer – fibrous: outermost layer of the eye with two portions that or continuous with one another
-Sclera: internal aspect of the fibrous tunic that forms the white portion of the eye with a layer of dense connective tissue acting as a point of attachment for extrinsic eye muscles.
-Cornea: external aspect of the fibrous tunic that is transparent to enable light transmission.

Question 38

Discuss the flow of aqueous humor.

Answer 38

Aqueous humour is produced by ciliary processes in the posterior chamber then sent through the pupil into anterior chambers to exit at the anterior chamber angle through trabecular meshwork into Schlemm’s canal and ultimately into episcleral venous channels that drain into the systemic circulation.

Question 39

What is glaucoma?

Answer 39

Glaucoma occurs when the flow of aqueous humour is blocked, causing excess fluid to accumulate in the chambers of the eye putting increased pressure on the structures and leading to damage of neural to neck and nerves. Symptoms include damage to the retina, reduced vision, and distortion of the optic nerve.

Question 40

What is responsible for hearing and equilibrium?

Answer 40

The receptors located in the inner ear are responsible for hearing and equilibrium, one’s unconscious sense of balance and position in space.

Question 41

Discuss the structure of the ear.

Answer 41

External ear: The structure of the ear that you can touch. Sound waves from the external environment travel through the external auditory canal to reach the tympanic membrane, causing it to vibrate. The tympanic membrane marks the boundary between the external and middle ear. Ceruminous glands are microscopic glands that are present in the external auditory canal as glands that secrete earwax.

Middle ear: Located within the temporal bone, spanning from the tympanic membrane to the oval window. Sound waves involved with hearing are transmitted through the middle ear.
-Tympanic cavity: chamber in the temporal bone
-Ossicles: small bones in the middle ear That transmit sound waves to the receptors in the inner ear with muscles that dampen loud noises. The malleus is the most lateral ossicle, The incus sits between the malleus and the stapes, and the stapes is the smallest bone that sits in the oval window (1/3 mass)
-Round and oval windows: areas at which the middle ear connects to the inner ear
-Eustachian tube: connects the middle ear to the nasopharynx

Inner ear: located within the temporal bone housing the receptor is responsible for hearing and equilibrium.
-Vestibular apparatus: contains receptors for equilibrium. Semicircular canals detect rotational movement, well utricle and saccule are responsible for detecting positional movement.
-Cochlea: contains receptors for hearing. A cross-section of cochlea reveals the structure has three ducts: the vestibular, tympanic, and cochlear. The organ of Corti is made up of specialized cochlear hair cells that rest on the basilar membrane to detect sound waves and fire an impulse to the brain via CNVIII for interpretation.

Labyrinth: both the cochlea and vestibular apparatus are structured as channels in the bone, called labyrinths. Both labyrinths are filled with fluid that allow us to hear or become aware of and monitor the position of her head. The membraneous labyrinth is within the boney labyrinth, filled with endolymph. Boney labyrinth is filled with perilymph.

Question 42

What is the endocrine system?

Answer 42

The endocrine system is a system of glands that secrete hormones into the bloodstream to create an effect. It impacts all the systems of the body.

Question 43

What are the different types of glands?

Answer 43

Endocrine: cells secrete hormones directly into the interstitial fluid surrounding the secretory cells. The hormones are then picked up by blood capillaries.

Exocrine: glands that secrete cell products into a duct system.

Question 44

What are hormones?

Answer 44

Hormones act as chemical messengers that travel through blood circulation to cause an affect on a target organ.

Question 45

Briefly discuss the endocrine glands.

Answer 45

Pituitary gland: small gland at the base of the brain that extends from the hypothalamus to produce and release hormones that control all other endocrine glands.

Thyroid gland: sits anterior to the trachea and produces thyroid hormones important for metabolism and maintaining calcium homeostasis.

Parathyroid glands: four small oval glands on the back of the thyroid that are paired and involved in the maintenance of calcium homeostasis.

Adrenal glands: paired glands that sit on top of each kidney to produce corticosteroids and maintain fluid balance.

Pancreas: and endocrine and exocrine gland located posterior to the stomach extending from the duodenum to the spleen with function to control sugar levels in the blood.

Question 46

Discuss the pituitary gland.

Answer 46

Pituitary gland is the master gland because it releases hormones that control all other endocrine glands. It is located inferior to the hypothalamus, sitting on a concavity of the sphenoid bone in the middle of the skull. The physical contact between the hypothalamus and the pituitary allows for communication between the nervous and endocrine systems.

Anterior lobe (Adenohypophesis): composed of glandular secretory cells that produce and release 7 stimulating hormones.
-TSH: causes thyroid gland to release thyroid hormones
-PRL: induces mammary glands of the breast to produce milk
-ACTH: causes adrenal glands to release their hormones
-GH: stimulates growth in all cells
-FSH/LH: act on the gonads to stimulate secretion of estrogen and progesterone, and maturation of oocytes in the ovaries. They also stimulates secretion of testosterone and sperm production in the testes.
-MSH: stimulates melanocytes in the skin to produce pigment

Posterior lobe (Neurohypophesis): made up of nervous tissue to release two hormones produced in the hypothalamus.
-ADH: promotes reabsorption of water at the kidneys
-Oxytocin: promotes uterine contractions during childbirth and plays a role in breast-feeding

Question 47

What is the histology of the pituitary gland?

Answer 47

Anterior: made of granular acini that are arranged in small groups surrounded by connective tissue. Stains darker.

Posterior: composed of nervous and connective tissue without acini. Stains lighter.

Question 48

Discuss the thyroid gland.

Answer 48

The thyroid gland sits in the neck anterior to the trachea and inferior to the larynx. It is important in maintaining metabolic homeostasis.

The thyroid gland is divided into the right lobe, left lobe, and isthmus (sits in between and connects the two lobes)

The thyroid gland is composed of follicles that are lined with simple cuboidal follicular cells surrounding a central lumen field with colloid. Between the follicles are parafollicular or C cells.

Follicular cells: produce T3 and T4 which act to increase the rate of metabolism and oxygen consumption.

C cells: produced calcitonin, a hormone which lowers the blood calcium concentration.

Question 49

What is a goitre?

Answer 49

A goitre is a physiological condition where the thyroid gland expands in size, causing a large lump in the neck. It is due to an excess or lack of thyroid hormones T3 and T4. The pituitary gland hormone that causes this is TSH.

Question 50

Discuss the parathyroid glands.

Answer 50

The parathyroid glands are for small oval glands on the posterior side of the thyroid. Thera paired with two superior glands and two inferior glands. Along with a thyroid gland they secrete hormones to contribute to calcium homeostasis.

Parathyroid glands are made up of principal/chief cells that produce PTH to increase calcium ion concentration in the blood.

Question 51

Discuss adrenal glands.

Answer 51

Adrenal glands are two pyramid shaped structures that sit superior to each kidney.

Adrenal cortex: divided into three layers that produce over two dozen hormones called corticosteroids. The outer layer produces hormones known as mineralocorticoids, the middle layer produces glucocorticoids, and the inner layer produces androgens (sex hormones).

Adrenal medulla: the core of the adrenal gland that produces epinephrine and norepinephrine in response to sympathetic nervous system stimulation resulting in autonomic fight or flight response.

Question 52

Discuss the pancreas.

Answer 52

The pancreas is a long lobular organ that lies posterior to the stomach with its medial and reaching the duodenum and the lateral end extending to the spleen. It produces enzymes for digestion and the hormone insulin to regulate blood sugar levels.

The pancreas is a mixed gland, meaning it has exocrine and endocrine functions. Endocrine functions are the result of specialized groups of cells in the pancreatic islets or islets of Langerhans. There are two main cell types:

Beta cells: produce insulin which functions to lower blood glucose levels (Hypoglycemic hormone)

Alpha cells: produces glucagon which functions to increase blood glucose levels (Hyperglycemic hormone)

Question 53

What are other endocrine glands?

Answer 53

Other endocrine glands include the thymus, digestive system, kidneys, gonads, and heart.