Structure of the Nervous System and Sensory Perception

Question 1

Slide 1: Cross section through the rat spinal cord

Examine the slide under low power (x4). With the aid of the diagram below, identify the dorsal and ventral fissures, the grey matter, the white matter, the anterior and posterior horns of grey matter, and the central canal.

Answer 1

Question 2

Locate the neuron cell bodies in the anterior horn of the grey matter. Use the diagram below to help you. Identify the large cell bodies with large, round, palely-stained nuclei and a prominent nucleolus, the axon and axon hillock and the nuclei of the neuroglia in the grey matter between the anterior horn nerve cells.

Answer 2

Question 2

Locate the neuron cell bodies in the anterior horn of the grey matter. Use the diagram below to help you. Identify the large cell bodies with large, round, palely-stained nuclei and a prominent nucleolus, the axon and axon hillock and the nuclei of the neuroglia in the grey matter between the anterior horn nerve cells.

Answer 2

Question 3

1. List and describe the structure and function of the components of the grey matter. (4)

Answer 3

In the brain, grey matter is used to process information.
Neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries are some of the elements that make up grey matter.

Question 4

What is the structure and function of the neuronal cell body?

Answer 4

The cell body maintains the structure of the neuron, houses genetic material, and supplies energy to power operations. A neuron’s soma has a nucleus and specialized organelles,
just like other cell bodies do. It is protected and given access to its local environment by a membrane
that surrounds it.

Question 5

What is the structure and function of the neuropil (dendrites and unmyelinated axons)?

Answer 5

Dendrites are short, narrow and highly branched
structures that receive signals from other neurons, to process these signals, and to transfer the
information to the soma of the neuron.

Question 6

What is the structure and function of the Glial cells (astrocytes and oligodendrocytes)?

Answer 6

Glial cells provide support and protection to the neurons
and have a fibrous appearance due to thick bundles of cytoplasmic filaments.

Question 7

What is the structure and function of synapses?

Answer 7

A synapse is the small gap between two neurons which enable to communicate with each
other.

Question 8

What is the structure and function of capillaries?

Answer 8

Very small blood vessels that are responsible for facilitating the transport and exchange of gases, fluids, and nutrients in the body.

Question 9

List and describe the structure and function of the components of the white matter. (2)

Answer 9

The myelinated axons that make up white matter are what give the substance its white color. These are in charge of sending electrical impulses between cells. The grey matter is encircled by white
matter.

Question 10

With the aid of the diagrams on the next page, identify the thin, blue-stained endoneurial sheath around each nerve fibre, the central unstained axons, the nodes of Ranvier and the nuclei of the neuroglia / neurillema / Schwann cells. Note the variation in the size of the nerve fibres.

Answer 10

Question 11

Label the vein, artery and perineurium.

Answer 11

Question 12

Label the axon, endoneurium and myelin.

Answer 12

Question 13

Where in the body are peripheral nerves found?

Answer 13

Everywhere besides the brain and spinal cord.

Question 14

Write a short paragraph on the structure and function of the myelin sheath. Include in your paragraph the formation of the myelin sheath and how myelination affects the speed of transmission of neural impulses. (5)

Answer 14

The Schwann cell in the PNS or the Oligodendrocyte in the CNS create the fatty layer known as the myelin sheath. Being fatty makes it a good insulator and a bad conductor of electricity. This guarantees that the myelin coating can protect the axon sufficiently. Its function is to control extracellular fluid, protect, insulate, and speed up electrical conduction.

Question 15

6. Multiple sclerosis (MS) is a chronic disease that affects neurons of the brain and spinal cord. MS causes a variety of symptoms, such as changes in sensation in the face and limbs, complete or partial loss of vision (optic neuritis), muscle weakness, unsteadiness when walking, speech difficulties, cognitive impairments and emotional instability. In point form, describe the pathophysiology of MS. (6)

Answer 15

• MS is a condition in which the body’s immune system attacks oligodendrocytes.
• This causes an inflammation of the neuron and leads to degenerated myelin sheath
• The myelin sheath without the oligodendrocytes die and are no longer reproduced
• This causes an exposure of the axons
• The axons are no longer insulated and the conduction of the electrical stimuli either becomes very
  slow or ceases to exist
• Because it affects the CNS, the conduction to and from the brain and/or spin is thus impaired which explains the numerous symptoms

Question 16

With the aid of the diagram below, locate a neuromuscular junction, the junction between a
neuron and the muscle. Identify the neuron with its Schwann cells, and the nerve terminals
that stimulate the muscle. (5)

Answer 16

Question 17

Label and annotate the diagram illustrated on the next page using the underlined terms. In addition, label the white matter and the grey matter. Note: The copy that must be labelled can be found at the end of the practical. (5)

Answer 17

A. Sensory Neuron: nerve cells that are activated by sensory input from the environment.

B. Dendrites: receive signals from other neurons, to process these signals, and to transfer the information to the soma of the neuron.

C. Cell body: of sensory neuron,in the dorsal root ganglion.

D. Interneuron: they carry sensory information and regulate motor activity.

E. Grey matter: contains a large number of unmyelinated axons which process and transport impulses.

F. White matter: contains myelinated nerve axons which transmits electrical impulses through the CNS.

G. Spinal cord: form part of the CNS.

H. Motor neuron: integrating signals from the brain to the effector muscles.

I. Motor neuron axon terminals: synapse with effector to bring about response

J Effector muscle: contracts to reduce harm to the body.

Question 18

What is the advantage of the spinal reflex? (2)

Answer 18

The signal does not need to pass through the brain in order to be understood, saving a significant amount of conduction time and allowing for fast reactions to avoid damaging receptors. By turning on spinal motor neurons, faster reflex responses can be triggered without having to wait
for signals to travel to the brain.

Question 19

Why do doctors test for the knee-jerk reflex? (2)

Answer 19

By doing so, it is determined whether the patient’s neurological system is responsive and fully functional. The neurological system is completely operational if the knee-jerk reflex is successful. There can be a problem with brain processing if there are processing lags.

Question 20

With the aid of the diagram below, locate a taste bud. Each taste bud consists of a taste pore, an opening on the tongue’s surface surrounded by epithelial cells. Below the taste pore are several sensory receptor cells that transduce chemical stimuli into neural (i.e. electrical) impulses. The receptor cells are linked to the CNS by sensory neurons.

Answer 20

Question 21

How are chemical stimuli transduced into electrical impulses and where else in the body are chemical stimuli converted into electrical impulses? (4)

Answer 21

• chemical stimuli is also converted into electrical impulse in the olfactory cell located within the nose
• a flavour enhancer called monosodium glutamate, which occurs naturally in the foods.
• receptors known as the gustation are responsible for converting the chemical stimuli into an electrical impulse which will be perceived in the brain as taste
• there are five different types of receptor cells

Question 22

Why are we unable to taste properly when we have a blocked nose, despite our tongues not being affected?

Answer 22

Taste and smell go hand in hand and are strongly tied to one another. The olfactory receptor nerve cells in the nose are capable of detecting specific molecules in food and scented objects, which are then translated into a perceived smell. Flavor and taste are both derived from smell, therefore when olfactory receptors are inhibited, taste is impacted.

Question 23

What are the advantages of adapting to a stimulus? (2)

Answer 23

After repeated exposure to a stimulus, the body becomes less sensitive to it, which is known as sensory adaptation. While sensory adaptation lessens our awareness of a stimulus, it lets us have more time and energy to focus on other environmental cues.

Question 24

What are the disadvantages of adapting to a stimulus? (2)

Answer 24

We reduce our sensitivity and awareness to stimuli which are common in our environment. This could potentially make us less aware of dangers around us.

Question 25

Explain, in your own words, why we cannot tickle ourselves.

Answer 25

The cerebellum can predict sensations when your own movement causes them but not when someone else does. When you try to tickle yourself, the cerebellum predicts the sensation and this prediction is used to cancel the response of other brain areas to the tickle.

Question 26

What is the blind spot?

Answer 26

The spot where your optic nerve connects to your retina has no light-sensitive cells, so you can’t see anything there.

Question 27

Why don’t you have an “empty space” in your field of vision all the time?

Answer 27

Our brain can usually fill in the information that we are missing based on the other things around the
blind spot.The brain can use estimation to project an image into the empty space so that we can have
a completed vision.

Question 28

What is accommodation?

Answer 28

This is a phenomenon where the eye changes to focus on certain objects at variable distances from the observer.

Question 29

How important is visual input in supplementing proprioceptors?

Answer 29

Proprioceptors need visual input since it tells them where we are and how we’re moving in relation to
our surroundings. This knowledge is necessary for proprioceptors to correctly coordinate balance and
govern body posture.

Question 30

Label the front of the eye.

Answer 30

Question 31

Label the back of the eye.

Answer 31

Question 32

Answer 32

Question 33

Answer 33

Question 34

List and describe the structures that make up a peripheral nerve. (4)

Answer 34

The structure of peripheral nerves includes: dendrites, myelinated axons, an endoneurium, perineurium and epineurium, as well as nerve fascicles and blood vessels (arteries and veins).

Question 35

Nerve Impulse Mechanism (8)

Answer 35

Question 36

Formation of the resting potential (RP)

Answer 36

1. A neuron at RP, the concentration of K+ is greater in cell while
   concentration of Na+ is greater in ECF.
2. A negative charge inside cell (due to anions in cell)
3. A positive charge outside cell
4. A neuron at RP contains multiple passive K+ channels and fewer Na+
   passive channels → K+ diffuses out of cell → cells are very permeable to K+
   and slightly permeable to Na+
5. The cell has to work to keep K+ inside cell to keep cell gradient
6. Neurons have a sodium-potassium pump → only allows 3 Na+ ions to exit
   cell and 2 K+ ions to enter cell → 3 Na+ going out helps generate + charge
   outside of cell
7. Sodium-potassium pump requires ATP energy (a chemical ligand which
   activates pump) to move Na+ and K+ against their concentration gradients
   and maintain gradient
8. ATP hydrolysis (ATP → ADP + Phosphate) causes phosphate group to bind
   to pump to allow change in shape, increasing its affinity to Na+ or K+.
9. As potassium binds (Na+ is transported ) and falls off (K+ is transported),
   shape changes.
10. Glucose is needed to undergo cellular respiration to produce ATP
11. Allows maintenance of (-) inside and (+) outside

Question 37

Action Potential series of Events (5)

Answer 37

Question 38

Synaptic Transmission (3)

Answer 38

1. Action potential arrives; triggers entry of Ca2+ into axon bulb of
   presynaptic neuron (voltage-gated Ca2+ channels)
2. In response to Ca2+, synaptic vesicles fuse with membrane, release
   neurotransmitter (synthesized by presynaptic neuron)
3. Neurotransmitters reach postsynaptic membrane by diffusion,
   chemically/ligand gated ion channels open when neurotransmitter binds,
   causes change in postsynaptic cell potential (graded potentials)

Question 39

What are the 3 major anatomical and functional divisions of the brain?

Answer 39

Question 40

Your cerebral cortex/forebrain has 4 functional lobes, which are?

(Integrates and interprets sensory information, memory, abstract thought,
awareness, control of skeletal muscle)

Answer 40