Chapter 3

Describe the role of the Golgi tendon organ in controlling muscle contraction.

Golgi tendon organs are sensitive to tension in the muscle-tendon complex and operate like a strain gauge, a device that senses changes in tension. When stimulated, these receptors inhibit the contracting (agonist) muscles and excite the antagonist muscles.

What brain centers have major roles in controlling movement, and what are these roles?

Primary Motor Cortex which controls frontal lobe and conscious control of skeletal muscle movements. The basal ganglia which controls cerebral white matter and helps initiate sustained/repetitive movement. Lastly the cerebrum which controls rapid and complex movements.

Central Nervous system:

System consisting of the brain and spinal cord.

Cholinergic:

Systems mediated by the neurotransmitter acetylcholine.

Name the different anatomical parts of a neuron and discuss their function.

The different anatomical parts of a neuron are the cell body (soma), dendrites, and axon. The cell body contains the nucleus. The dendrites receive action potentials and the axon are terminals or knobs that house numerous vesicles (sacs) filled with chemicals knowns as neurotransmitters that are used for communication between a neuron and another cell.

Norepinephrine:

a catecholamine released from the adrenal medulla that, along with epinephrine, prepares the body for a fight or flight response. It is also a neurotransmitter.

Neurotransmitter:

a chemical used for communication between a neuron and another cell.

Depolarization:

a decrease in the electrical potential across a membrane, as when the inside of a neuron becomes less negative relative to the outside

Excitatory postsynaptic potential (EPSP):

a depolarization of the postsynaptic membrane caused by an excitatory impulse.

Inhibitory postsynaptic potential (IPSP):

a hyperpolarization of the postsynaptic membrane caused by an inhibitory impulse.

Graded potential:

a localized change (depolarization or hyperpolarization) in the membrane potential.

Threshold:

a minimum amount of stimulus needed to elicit a response. Also, the minimum depolarization required to produce an action potential in neurons.

Motor nerves/motor neurons:

efferent nerves that carry impulses to skeletal muscle.

How do the sympathetic and parasympathetic systems differ? What is their significance in performing physical activity? Sympathetic = fight or flight

increases HR rate and contraction strength, dilates blood vessels, BP increases, increased bronchodilation Parasympathetic: rest or digest digestion, urination, glandular secretion and conservation of energy

Nerve impulse:

the electrical signal conducted along a neuron, which can be transmitted to another neuron or an end organ such as a group of muscle fibers.

Synapse:

the junction between two neurons

Saltatory conduction:

the means of rapid nerve impulse conduction along myelinated neurons

Effector (efferent) nerves:

the motor division of the peripheral nervous system, carrying impulses from the CNS toward the periphery.

Myelin Sheath:

the outer covering of a myelinated nerve fiber, formed by a fatlike substance called myelin.

Resting membrane Potential (RMP):

the potential difference between the electrical charges inside a cell and outside the cell, caused by a separation of charges across the membrane.

Sensory-motor integration:

the process by which the sensory and motor systems communicate and coordinate with each other.

Peripheral nervous system (PNS):

the section of the nervous system through which motor nerve impulses are transmitted from the brain and spinal cord to the periphery and sensory nerve impulses are transmitted from the periphery to the brain and spinal cord.

Neuromuscular junction:

the site at which a motor neuron communicates with a muscle fiber.

End branches:

branches coming off the ends of the axons leading to the axon terminals.

Explain how reflex movement occurs in response to touching a hot object.

First the stimuli of heat and pain are received by the thermoreceptors and nociceptors in the hand, and then sensory action potentials travel to the spinal cord, terminating at the level of entry. Once in the spinal cord, these action potentials are integrated instantly by interneurons that connect the sensory and motor neurons. The action potentials move to the motor neurons and travel to the effectors, the muscles controlling the withdrawal of the hand. The result is that the person reflexively withdraws the hand from the hot stove without giving the action any thought (pg. 89)

Describe an action potential. What is required before an action potential is activated?

Membrane depolarizes from the RMP of -70mV to -55mV (threshold; graded potential becomes an AP)Voltage gated Na+ channels open and Na+ enters cell and cell further depolarizes to -10mV. K+ moves from cell into extracellular fluid and cell is repolarized and eventually returns to RMP

Describe the role of the muscle spindle in controlling muscle contraction.

Muscle spindle is innervated by gamma motor neurons. Its synapses in the spinal cord with an alpha motor neuron and triggers reflex muscle contraction. Helps to prevent further damaging stretch.

Explain the resting membrane potential. What causes it? How is it maintained?

The resting membrane potential is the potential difference between the electrical charges inside a cell and outside a cell. It is caused by an uneven separation of charge ions across the membrane. The RMP is maintained in two ways. First, the cell membrane is much more permeable to K+ than to Na+, so the K+ can move more freely. Secondly, sodium-potassium pumps in the neuron membrane, which contain Na+-K+ adenosine triphosphate., maintains the imbalance on each side of the membrane by actively transporting potassium ions in and sodium ions out.

What are the major divisions of the nervous system? What are their major functions? The major divisions of the nervous system are the CNS (central nervous system) and the PNS (peripheral nervous system).

The sensory nerves of the PNS are responsible for informing the CNS about what is going on within and outside the body.

Axon hillock:

a part of the neuron, between the cell body and the axon that controls traffic down the axon through summation of excitatory and inhibitory postsynaptic potentials.

Acetylcholine:

a primary neurotransmitter that transmits impulses across the synaptic cleft

Golgi Tendon organ:

a sensory receptor in a muscle tendon that monitors tension.

Muscle spindle:

a sensory receptor located in the muscle that sense how much the muscle is stretched.

Neuron:

a specialized cell in the nervous system responsible for generating and transmitting nerve impulses.

Sensory (afferent) neurons:

afferent nerves that carry impulses toward the central nervous system from the periphery.

Sodium-potassium pump:

an enzyme called Na+-K+-ATPase, which maintains the resting membrane potential in disequilibrium at -70mv

Hyperpolarization:

an increase in the electrical potential across a membrane.

Motor Reflex:

an involuntary motor response to a given stimulus.

Explain how an action potential is transmitted from a presynaptic neuron to a postsynaptic neuron. Describe a synapse and a neuromuscular junction.

nerve impulse from presynaptic neuron reaches axon terminal, which stimulates the release of neurotransmitters into the synaptic cleft from synaptic vesicles each neurotransmitter binds to a postsynaptic receptor which initiates a series of graded potentials A alpha-motor neuron communicates with its muscle fibers at a neuromuscular junction - functions the same as synapse EXCEPT axon terminals protrude into end motor plates which are invigilated segments on the plasmalemma of the muscle finer.

Axon terminal:

one of numerous branched ending s of an axon. Also known as a terminal fibril.

Adrenergic:

refers to norepinephrine or epinephrine