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Tiara Lazuardi

Biology 12

 

Prescribed Learning Outcome

The Nervous System

Neuron to Reflex Arc

  1. Identify and give functions for the following: dendrite, cell body, and axon

    2. Dendrite: part of a nerve cell which conducts signals toward the cell body

    Cell body: part of a nerve cell which contains the nucleus

    Axon: part of a nerve cell which conducts impulses away from the cell body

  2. Distinguish between sensory, motor, and interneuron with respect to structure and function

    3. Sensory neuron (afferent neuron): type of neuron which takes a message from a sense organ to the CNS

    Motor neuron (efferent neuron): type of neuron which takes a message away from the CNS to an effector (muscle or gland), it has short dendrites and a long axon

    Interneuron (association): type of neuron found completely within CNS which conveys messages between parts of the system; has short dendrites and long/short axon

  3. Explain transmission of a nerve impulse through a neuron, using the following terms:
  1. Resting and action potential: resting potential is the polarity across the plasma membrane of a resting neuron due to an unequal distribution of ions (-65mV), action potential is polarity changes due to the movement of ions across the plasma membrane of an active neuron. Action potential can be caused by stimulation by an electric shock, a sudden difference in pH, or a pinch.
  2. Depolarization and repolarization: depolarization occurs when stimulation of an axon causes the gates of sodium channels to open temporarily (becomes permeable), allowing Na+ ions to flow into the axon; this causes the action potential to swing up to +40mV. Repolarization occurs when the potassium gates open and K+ leaves the inside of the axon, causing the action potential swing to drop from +40mV to –65mV.
  3. Sodium and potassium gates (refer to above)
  4. Sodium-potassium pump: a protein carrier which pumps Na+ out and K+ across the axon membrane. It is always working.
  5. Recovery period: also known as a refractory period whereby a fiber cannot conduct an impulse; occurs right after an impulse has been conducted; insures one-way direction of impulse.
  6. Threshold ("all-or-none response"): once a neuron has reached threshold (-20mV), it sends the impulse through the fiber maximally.
  1. Relate the structure of a myelinated nerve fiber to the speed of the impulse conduction

    2. Schwann cells (neurolemmocytes) are neuroglial cells which encircle a fiber, leaving gaps called the nodes of Ranvier (neurofibril nodes). Schwann cells wrap themselves around the axon many times, and in this way lay down several layers of plasma membrane containing myelin, which forms a myelin sheath. Impulses travel through a fiber by jumping from node to node. This is called saltatory conduction. It allows rapid conduction (200m/sec).

  2. Identify the major components of a synapse

    3. Axon bulb is the small swelling on an axon branch, lying very close to the dendrite/cell body of another nuron.

    Presynaptic membrane is the membrane of the first neuron (the axon).

    Postsynaptic membrane is the membrane of the next neuron (the dendrite).

    Synaptic cleft is the small gap between the presynaptic and postsynaptic membrane.

    Neurotransmitters are chemicals stored at then ends of axons in vesicles that is responsible for transmission across a synapse, by causing excitation (causes Na+ channels to open; neuron transmits a nerve impulse) or inhibition. Two neurotransmitters are acetylcholine (ACh) are norepinephine (NE).

  3. Explain the processes by which impulses travel across a synapse
  1. Nerve impulses travel along an axon; reaches axon bulb
  2. Ca+ enters the bulb; cause synaptic vesicles to merge with the presynaptic membrane
  3. Neurotransmitters released into synaptic cleft
  4. Neurotransmitter molecules diffuse across the cleft to the postynaptic membraneà bind with a receptor in a lock-and-key manner
  5. Neurotransmitters cause Na+ gates to open (impulse is carried) of the next neuron
  1. Demonstrate knowledge of how transmitters are broken down in the synaptic cleft

    2. The postsynaptic membrane contains enzymes that rapidly inactivate the neurotransmitter. For example, acetycholinesterase (AChE) breaks down acetylcholine. Sometimes, the synaptic ending rapidly reabsorbs the neurotransmitter, possibly for repackaging in a synaptic vesicle or for chemical breakdown.

  2. Relate the structure of a reflex arc to how it functions

Reflex arc is an automatic, involuntary response to changes occurring inside or outside the body. It involves the spinal chord and a spinal nerve.

  1. Receptor generates nerve impulses
  2. Impulse moves along sensory neuron toward the cell body and the CNS. The cell body of this sensory neuron is in the dorsal-root ganglion, outside the spinal chord (CNS).
  3. Impulse moves along cell body, along sensory neuron and enters spinal cord dorsally
  4. Impulse pass to many interneurons
  5. Impulse pass to a motor neuron in spinal chord
  6. Impulse leaves through axon, which leaves spinal chord ventrally
  7. Impulse travel along the axon to an effector
  8. Effector brings response to stimulis

 

Divisions and the Brain

  1. Contrast the locations and function of the central and peripheral nervous systems

    2. CNS consists of the spinal cord and the brain where nerve impulses are received, coordinated, and interpreted. Contains cell bodies.

    PNS located outside the midline of the body; contains nerves. Contains cranial nerves, spinal nerves, therefore sensory fibers, and motor fibers. The motor fibers are involved in the somatic and autonomic system. The somatic system involves nerves sending sensory impulses from receptors to the CNS and send motor impulses from the CNS to the skeletal muscles. In the autonomic system, consisting of the sympathetic and parasympathetic systems, motor impulses travel to smooth muscle, cardiac muscle, and the glands.

  2. Differentiate between the function of the sympathetic and parasympathetic divisions of the autonomic nervous system

    3. Sympathetic system is associated with "fight or flight" emergency responses. It accelerates the heartbeat, dilates the bronchi, and inhibits the digestive tract.

    Parasympathetic system is the "housekeeper system" in that it promotes all the internal responses associated with a relaxed state. It causes the pupil of the eye to contract, promotes digestion of food, and retards heartbeat.

  3. Identify the source gland for adrenaline and explain its role in the "fight or flight" response

    4. Source gland: adrenal medulla.

    -Increase blood glucose level, increases metabolic rate

    -Bronchioles dilate and breathing rate increases

    -Blood vessels to the digestive tract and skin constrict; those to skeletal muscles dilate

    -Cardiac muscle contracts more forcefully and heart rate increases

  4. Identify and give functions for each of the following:
  1. Medulla oblongata: part of the brainstem. Center of autonomic systems. Involved w/heartbeat, homeostasis, blood pressure. Initiates the "fight or flight" response. Contains vital centers for regulating heartbeat, breathing, and vascoconstriction. It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing.
  2. Cerebrum: conscious part of brain, center of nervous system thinking, controls central nervous system. Involved with sensory perception, learning, memory, skeletal muscle control. It is the largest part of the brain. The left side is involved with verbal tasks. The right side is involved with artistic talents.
  3. Thalamus sorts and relay sensory stimuli. Receives all sensory impulses and channels them to appropriate regions of the cortex for interpretation.
  4. Cerebellum: involved with muscle coordination, balance, posture, muscle tone.
  5. Hypothalamus: maintains homeostasis, and contains centers for regulating balance, and blood pressure. Controls pituitary gland; serves as link between nervous and endocrine system.
  6. Corpus callosum: connects the right and left of the brain; channels information between the two hemispheres.
  1. Explain how the hypothalamus and pituitary gland interact as the neuroendocrine control centre

There are neurons in the hypothalamus that are called neurosecretory cells because they respond to neurotransmitters and also produce hormones. They pass through axons that run between the hypothalamus and the posterior pituitary. These hormones are stored in axon endings. For example, neurosecretory cells in the hypothalamus produce and release the hormones ADH and oxytocin, which are stored in the posterior pituitary.

The hypothalamus controls the anterior pituitary by producing hypothalamic-releasing and release-inhibiting hormones. Each type of hypothalamic hormone either stimulates or inhibits production and secretion of a specific anterior pituitary hormone. The anterior pituitary secretes these different types of hormones into the blood stream.