Essay Questions

Question 1

Present 5 anatomical and/or physiological facts indicating that the Central Nervous System is quite unique in comparison to the other systems in the mammalian body.

Answer 1

1. It is the only organ system completely encased by bones and meninges
2. Most neurons do not divide through mitosis (amitotic)
3. Fat is conducive to brain health
4. The blood brain barrier prevents many toxins from entering the brain
5. Although it only accounts for 2% of total body weight, CNS uses 15% of body’s total oxygen and about 15% of blood in the body is in the CNS at any one time

Question 2

What are the seven common processes involved in neurotransmission?

Answer 2

1. Synthesis (small molecule NTs are synthesized in the cytoplasm)
2. Storage (small molecule NTs are packed in synaptic vesicles in the terminal button by the Golgi complex; these vesicles are stored in clusters next to the presynaptic membrane)
3. Enzymatic degradation of neurotransmitter leakage from the cytoplasm
4. Exocytosis (synaptic vesicles full of NTs hang out near the presynaptic membrane that is full of voltage-activated calcium channels. when stimulated by AP, the channels open, Ca2+ enters the button, causing the vesicles to fuse to the member, releasing the NTs)
5. Inhibitory feedback through autoreceptors (negative feedback); (autoreceptors bind to their neuron’s own NT molecules and they are located on the presynaptic membrane; monitor the number of NTs in the synapse; they reduce number when levels are high and increase when levels are low)
6. Activation of postsynaptic receptors (NTs produce signals by binding to receptors in postsynaptic membrane; each receptor is a protein that contains binding sites for only particular NTs, only impacts cells with receptors for it; NT is a ligand for its receptor)
7. Deactivation by either reuptake (drawn back into the presynaptic buttons by transporter mechanisms) or enzymatic degradation (broken apart by enzymes)

Question 3

Describe three main principles of converting environmental stimuli and their physical properties to neurological events.

Answer 3

The process of sensation and perception

1. Sense: sense the environmental stimuli using sensory organs which collect filter and amplify information.; the process of detecting the presence of stimuli; process of informing the brain about its environment
2. Percept: the final mental representation of the original environmental stimuli; the higher-order process of integrating, recognizing, and interpreting patterns of sensation
3. Transduction: conversion of stimuli detected in receptor cells to electrical impulse which are transported by the nervous system; changing a sensory signal to an electrical signal

Dr. Schwartz says slide 3 lecture 5

Question 4

Identify the main structural and physiological differences between the Sympathetic and the Parasympathetic divisions of the Autonomic Nervous System. What are their main functional contributions to the organism?

Answer 4

• Point of exit - The Sympathetic division exits through the thoracolumbar system, and the parasympathetic exits either through the cervical region and sacral region.
• Length of the presynaptic axon - In the sympathetic division, the presynaptic axon is myelinated and short as opposed to the parasympathetic nervous system the presynaptic axon is unmyelinated and long.
• Neurotransmitters - sympathetic division utilizes acetylcholine in preganglionic synapse and norepinephrine and/or epinephrine at the organ, whereas the parasympathetic division uses acetylcholine at all synapses.
• Actions at end organ sites (antagonistic) - contribution of the sympathetic division is to prepare for action (i.e., fight, flight, or freeze) (e.g., dilates pupils, increase metabolic rate, increase rate and force of heart rate, etc.).
• The main functional contributions of the parasympathetic division is to return to a normal state after fight, flight, or freeze (e.g., constricts pupils, decreases heart rate to be slow and steady, etc.)

Structural:

1. Part of spinal cord they exit (parasympathetic is cervical and sacral; sympathetic is thoracic and lumbar)
2. Parasympathetic synapses (aka ganglion) are closer to the effector organ (sympathetic are closer to the CNS in the adrenal medulla)
3. Parasympathetic axons are unmyelinated (both are unmyelinated postganglionic)

Physiological:
4. always starts with Acetylcholine (para stays with acetycholine because it is an inhibitor; sympathetic changes to norepinephrine because int is excitatory)

Sympathetic systems stimulate, organize, and mobilize energy in threatening situations; changes are indicative of psychological arousal (e.g., dilates pupils, inhibits salivary glands, decrease urine output)

Parasympathetic systems: conserve energy; indicative of psychological relaxation (e.g., constricts pupils, decrease heart rate)

Question 5

What is homeostasis? What is a homeostatic control mechanism and what are the main components and processes of this mechanism?

Answer 5

• Homeostasis is the body’s ability to maintain relatively stable internal conditions, in spite of continuously changing external environments.
• Homeostasis is not an unchanging state nor equilibrium, but a dynamic steady state; homeostasis is a relatively stable disequilibrium.
• Maintains internal stability and is how the organism is maintaining some sense of stability.

Homeostatic control mechanism:
Requires finely tuned communication within the body systems. Most homeostatic processes are accomplished by the highly efficient Nervous and Endocrine Systems.

• Each of the homeostatic control mechanisms have at least three components involved in regulating a particular variable (factor, event, process) not to stray from a setpoint (optimum value)
  1. A receptor that senses and monitors environmental stimuli
  2. An integrating control center determines needed set point, analyzes input and determines the appropriate response to environmental changes (stimuli)
  3. An effector offers the means by which the control center responds.

Negative feedback: product of the Rx leads to decrease in the Rx

–Homeostatic mechanisms rely on response loops (from stimulus to response) and feedback loops who modulate response loops.

• -Most homeostatic mechanisms are operated through negative feedback loops, which support homeostatic processes; positive feedback loops are rarely homeostatic.
• -For all practical purposes, all illnesses can be considered as homeostatic imbalances.

Stimulus produces change in variable –> change detected by RECEPTOR (sensor) –> input: information sent along afferent pathway to CONTROL CENTER –> output: information sent along efferent pathway to acting EFFECTOR –> response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis

Question 6

What are the three principles of sensorimotor functions? Offer specific functional ramifications of these principles.

Answer 6

1. Sensorimotor system is hierarchically organized – info flows from highest to lowest level of operation using multiple paths, while maintaining functional segregation of its neuronal units
   - -ramifications: System is adaptable and plastic, capable of acting with various degrees of involvement from the executive suite (cortex)

Hierarchy–pyramid

• levels of operation
• multiple pathways (each is specified but they can be interconnected)
• functional segregation

2. Motor output is guided by sensory input – the efficiency and goal-directedness of each movement is guided by a systemic use of continuous sensory feedback
   - -ramifications: Sensory and motor are constantly informing each other such (e.g. vision may require moving eyes; grabbing something involves feeling and sensing it)–sensory feedback

Output + input work together

• need to work together
• cant move mouth if numb
• movement is an integration of motor and sensory

3. Learning changes the nature and locus of sensorimotor control – learning and practice allows the system to organize responses in continuous sequences of action responding appropriately to sensory feedback without conscious regulation
   - -ramifications: Can develop internal schemas and muscle memory once we have developed proficiency in a task. At that point, can be disrupted by “overthinking”

Muscle memory

• during learning learning, cortex is constantly activated
• highly learned, less cortex, subcortical structures take over
• it means your cortex is free for new information–develop internal schema (adaptation)

Question 7

Describe the glial cells in the Nervous system (structure and function).

Answer 7

1. Astrocytes: (CNS) star-shaped, w/ arm-like extensions; function in protection (BBB); cover the outer surface of blood vessels in the brain and make contact with neurons; role in BBB blocking and allowing passage of chemicals; ability to contract or relax blood vessels based blood flow demands; can modulate neural activity; involved in synaptogenesis; ***involved in scaffolding, immune response, relate interstitial fluid (homeostasis), they prevent large chemicals from leaving the blood vessels and entering the brain, clear out synapses
2. Radial glia: astrocyte shoots out extension for a neuron to send axon across to aid in neural growth. After this function is complete, extension withdraws, resumes its function as an astrocyte; progenitor cells that can generate neurons, astrocytes, and oligodendrocytes;
   radial migration during neural tube development and later can differentiate (thought to be similar to stem cells)
3. Microglia: (CNS); mobile, small; involved with injury or disease by multiplying, engulfing cellular debris or even whole cells, and triggering inflammatory response; recently shown to play role in regulation of cell death, synapse formation, and synapse elimination
4. Ependymal cells (CNS): form walls; epithelial lining of ventricle cavities; epithelial layer that surrounds the choroid plexus; and the BBB (+ astrocytes); some have cilia that direct the CSF
5. Oligodendrocytes: make myelin sheath of axons inside brain (CNS); cells have extensions that are thick in myelin, these wrap around the axons, creating myelin sheaths
6. Schwann cells: make myelin sheath in spinal nerves, cranial nerves (PNS)
7. Satellite cells: similar roles to astrocytes in the CNS; supportive cells (PNS)