Final exam

Question 1

What are the essential components of a reflex arc?

Answer 1

1) Sensory receptor: Reposnds to a stimulus by producing a generator or receptor potential
2) Sensory neuron: Axon conducts impulses from receptor to integrating center
3) Integrating center : One or more regions within CNS that relay impulses from sensory to motor neurons
4) Motor neuron : Axon conducts impulses from integrating center of effector
5) Effector : Muscle or gland that respond to motor impulses

Question 2

How a monosynaptic reflex differs from a polysynaptic reflex?

Answer 2

Monosynaptic : Reflex arc has only one synapse in its path

Polysynaptic : Reflex arc has more than one synapse in its path

Question 3

Give an example of each type of reflex.

Answer 3

Stretch reflex: Knee jerk, controls muscle length by causing muscle contraction
Tendon reflex : Causes inhibition of the contration of the agonistic muscle
Flexor (withdrawal) reflex : Contaneoussensory stimuli causes the flexor muscle of the limb on same side to contract
Crossed-extensor reflex : Opposite limbs starts to extend after the beginning of flexor reflex.

Question 4

Give examples (and explain) of polysynaptic, intersegmental, and contralateral reflex.

Answer 4

Polysynaptic : Reflec arc have more one synapse in its path

Intersegmental: Flexor reflex (only one side of the spinal cord is involved, muscle flexing), Crossed-extensor reflex (on the other side the extensor is happening)

Segmental reflex: (stretch reflex and tendon reflex

Question 5

Briefly explain how the spinal cord is supported and protected inside the body.

Answer 5

Protected by: bones (vertebrae) and ligament.
Meninges : Dura mater (attached to endosteum at foramen magnum; filum terminale externum periosteum of coccyx) and denticulate ligaments.
Fluid (cerebrospinal fluis)

Question 6

How the spinal cord is secured to dura mater and how the spinal dura mater is secured to the vertebral column?

Answer 6

By the dura mater (outer tough sheath made of dense connective tissue).
Dura mater continues as epineurium in spinal nerves.

Question 7

Briefly describe the anatomical features observed in a transverse section of the spinal cord.

Answer 7

Gray matter and white matter

Question 8

What are the main functions of the gray matter and white matter in the spinal cord?

Answer 8

Gray matter : Responsible for integration of information (spinal reflexes); execute motor command from motor cortex

White matter : Bundles of axons running in parallel along the vertical direction connects different segments of the spinal cord and spinal cord with brain

Question 9

What functional deficit will you expect when the anterior root of the spinal nerve is damaged?

Answer 9

Damage of anterior root of spinal nerve (lower motor neuron) : Flaccid paralysis with loss of reflexes

Question 10

Briefly describe the structure of a muscle spindle.

Answer 10

3-10 mm long. Consist of 3-12 tiny intrafusal muscle fibers contained within a capsule made of connective tissue. Located throughout the muscle belly

• Annulospiral ending (nerve fiber type la - fast conducting. Present on both nuclear bag and nuclear chain fibers)
• Flower spray ending (nerve fiber type 2 - slower)

Question 11

How the sensory stimulus for a muscle spindle differs from the sensory stimulus for the Golgi tendon organ?

Answer 11

Muscle spindle responds to stretch while Golgi tendon organ responds to tension in the skeletal muscle.

Question 12

Mention one main function of gamma motor neurons.

Answer 12

• They prevent the spindle reflex from opposing voluntory contraction / streching
• Maintains proper damping function of muscle spindle regardless of the change in muscle length.

Question 13

What is the role of indirect motor pathways in regulating motor functions?

Answer 13

Indirect motor pathways deliver signals to LMNs from motor centers via nuclei in brain stem etc. control posture, balance and muscle tone

Question 14

Name the ion channels that are primarily responsible for generating resting membrane potential, receptor potential, and an action potential

Answer 14

Resting membrane potential: Leak channels
Receptor potential: Ligand-gated channel
Action potential: Voltage-gated channel.

Question 15

Give examples of two neurotransmitters that generate EPSPs (excitatory postsynaptic potential) and another two neurotransmitters that generate IPSPs (inhibitory postsynaptic potential) at the postsynaptic terminal.

Answer 15

ESPS : Glutamate , aspartate, cysteic acid

IPSP : Gamma amino butyric acid (GABA) , glycine

Question 16

How a graded potential differs from an action potential?

Answer 16

Action potential : Sequence of self-generating fast depolarization and repolarization of membrane potential that results in the propagation of a nerve impulse along the cell membrane.
Graded potential : The amplitude of the potential changes with stimulus intensity, allows summation important for information processing in CNS.

Differences based on:

• Origin
• Types of ion channels involved
• Conduction
• Amplitude of signal
• Duration
• Polarity
• Refractory period- present/absent

Question 17

As the spinal nerve exits through the intervertebral foramen, which structures in the nerve are the continuation of different meningeal layers of the spinal cord?

Answer 17

Dura mater (Outer tough sheath made of dense connective tissue)
Arachnoid mater (middle thin layer of made of cells, loose collagen and elastic fiber) 
Pia mater (innermost layer, adhered to spinal cord, blood vessels present under this layer)
-Arachnoid / piamater continues as perineurium in spinal nerves.

Question 18

How a clinician can determine whether a muscle paralysis is due to damage in the upper motor or lower motor neurons?

Answer 18

Damage of upper motor neuron: Spastic paralysis (increased muscle tone) and exaggerated reflexes.

Damage of lower motor neuron: Flaccid paralysis with loss of reflexes.

Question 19

. Using a flowchart, describe how a voluntary motor command for distal limb muscles travels from the motor cortex to the effector muscles.

Answer 19

Lateral corticospinal pathway -from the primary mortor area – midbrain – pons – medulla- pyramid- crossing – lateral corticospinal – lower motor neuron

Anterior corticospinal pathway – do not cross, go on the same side

Sensory pathways - Posterior column and anterolateral pathway

Question 20

Will the same neuronal pathway be followed for the control of proximal limb muscles?

Answer 20

NO, Anterior – proximal limb, lateral = distal

Question 21

What is the role of indirect motor pathways in regulating motor functions?

Answer 21

In indirect pathways upper motor neurons originate from various motor nuclei in the brain stem: helps in maintaining posture, balance, muscle tone, reflexive movement to visual or auditory stimuli

Question 22

Draw the trace of an action potential and label its different phases. Mention the states (close/open) of voltage-gated Na+ and K+ channels at each phase.

Answer 22

SEE PICTURE OF THE GRAPH

Question 23

What are the mechanisms by which unequal distribution of ions is established across the two sides of the neuronal plasma membrane?

Answer 23

• Active transport of ions (sodium-potassium ATPase pump):
• -Creates ionic concentration gradient
• -Contributes to overall negative charge inside

-Donnan equilibrium (due to the presence of impermeable charged particles one side of mebrane)

Question 24

Explain why the neurons have a resting membrane potential close to -70 mV.

Answer 24

K+ leak channels are much more abundant than leak channels for other ions and therefore the resting membrane potential is largely determined by the K+ leak channels with minimal contributions from Na+ and Cl- leak channels.

Question 25

Mention the major differences between a graded potential and an action potential.

Answer 25

Differences based on (a) Origin, (b) types of ion channels involved, (c) Conduction, (d) Amplitude of signal, (e) Duration, (f) Polarity, (j) Refractory period- present/absent.

Question 26

What are the two main mechanisms for the propagation of action potential?

Answer 26

• Continuous AP propoagation

- Saltatory AP propagation

Question 27

Which one of these provides faster conduction of nerve impulse along the axon?

Answer 27

Saltatory AP propagation

Question 28

Describe briefly the steps of action potential propagation by this mechanism.

Answer 28

Saltatory conduction of AP:

• An action potential generated in a node of Ranvier causes influx of Na+ ions
• Na+ ions diffuse through the axoplasm to the next node and induces a depolarizing graded potential.
• When the depolarization in the second node exceeds the threshold potential, an action potential is generated there due to the high density of voltage-gated Na+ and K+ channels in the node.
• No action potential is generated in the myelinated region due to a low concentration of voltage-gated ion channels there.

Question 29

Name the main cell types found in the neural layer of the retina and briefly describe (you can use a flowchart) how a light stimulus on retina generates a nerve impulse in the optic nerve.

Answer 29

Rods enable vision in dim light; rod cells are distributed in both central and peripheral part of the retina
Cones are active under bright light only; generates sharper image and color vision; cone cells are concentrated in the central part of retina.
Pigmented epithelium: absorbs light and prevents light from reflecting back from retina

In darkness, rod photoreceptors release glutamate that acts as inhibitory neurotransmitter (note glutamate is excitatory in other systems); in presence of light glutamate release is inhibited
Hyperpolarization of bipolar cells in response to glutamate inhibits them from transmitting signals to ganglion cells which provide output from the retina to the brain.

Question 30

Why the visual acuity (sharpness of vision) is highest at the fovea centralis?

Answer 30

Many cone cells

Question 31

An eye is often compared with a camera for the process by which light coming from an object forms an image on the retina. Name the structures in the eye that light must travel through before it reaches the photoreceptors on retina

Answer 31

The LENS can accommodate (that is able to change the focal length by changing its curvature) to properly focus the object. Lens curvature is increased when ciliary muscles contract.

Question 32

. How the eyes are able to focus on objects located at different distances and also can adjust the amount of light entering into the eye?

Answer 32

The amount of light entering the eyes are regulated by pupillary diameter. Contraction of circular muscle in the iris cause pupillary constriction.

Question 33

Explain why distant and near objects appear blurred in myopic and hypermetropic eyes, respectively.

Answer 33

• Reduced size of the pupil improves depth of focus – objects located far from focus appear more sharp
• The image of a focused object is projected onto the central fovea, the site where vision is the sharpest.

Question 34

What are the major differences between somatic and autonomic motor neuron supply to an effector organ in terms of structural organization?

Answer 34

One single motor neuron connects spinal cord/brain stem nuclei to effector
The motor neuron is highly myelinated (axon diameter larger) and conduction speed is high
The synapse in the effector organ (skeletal muscle) have well-defined synapse structure with nicotinic (ionotropic) acetylcholine receptors present at post-synapse.

Question 35

Give one example of an effector organ for each where only sympathetic or parasympathetic motor innervation is observed.

Answer 35

Sympathetic supply alone: Sweat glands, arrector pili muscles
Parasympathetic supply alone: Ciliary muscles in the eye