Ch. 17

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What are the parts and correct order of the reflex arc?

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A reflex arc is a neural pathway that controls an action reflex. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs.

Nerve impulses propagating into, through, and out of the CNS follow specific pathways, depending on the type of information, its origin, and its destination. The pathway followed by nerve impulses that produce a reflex is a reflex arc [Pronunciation] (reflex circuit). Using the patellar reflex (knee jerk) as an example, the basic components of a reflex arc are as follows (Figure 17.12):
1. Sensory receptor. The distal end of a sensory neuron (dendrite) or an associated sensory structure serves as a sensory receptor. Sensory receptors respond to a specific type of stimulus (a change in the internal or external environment) by generating one or more nerve impulses. In the patellar reflex, sensory receptors known as muscle spindles detect slight stretching of the quadriceps femoris muscle (anterior thigh) when the patellar (knee cap) ligament is tapped with a reflex hammer.
2. Sensory neuron. The nerve impulses conduct from the sensory receptor along the axon of a sensory neuron to its axon terminals, which are located in the CNS gray matter. From here, relay neurons send nerve impulses to the area of the brain that allows conscious awareness that the reflex has occurred.
3. Integrating center. One or more regions of gray matter in the CNS act as an integrating center. In the simplest type of reflex, such as the patellar reflex in our example, the integrating center is a single synapse between a sensory neuron and a motor neuron in the spinal cord. A reflex pathway in the CNS that involves one synapse is called a monosynaptic reflex arc (mon′‐ō‐si‐NAP‐tik; mono‐=one). In other types of reflexes, the integrating center includes one or more interneurons and thus more than one synapse. These reflex pathways are referred to as polysynaptic reflex arcs (poly‐=many).
4. Motor neuron. Impulses triggered by the integrating center pass out of the spinal cord (or brain stem, in the case of a cranial reflex) along a motor neuron to the part of the body that will respond. In the patellar reflex, the axon of the motor neuron extends to the quadriceps femoris muscle. While the quadriceps femoris muscle is contracting, the antagonist hamstring muscles are relaxed.
5. Effector. The part of the body that responds to the motor nerve impulse, such as a muscle or gland, is the effector. The patellar reflex is a somatic reflex because its effector is a skeletal muscle, the quadriceps femoris muscle, which contracts and thereby relieves the stretching that initiated the reflex. In sum, the patellar reflex causes extension of the knee by contraction of the quadriceps femoris muscle in response to tapping the patellar ligament. If the effector is smooth muscle, cardiac muscle, or a gland, the reflex is an autonomic (visceral) reflex

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what do you find in the white matter of the spinal cord?

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The white matter surrounds the gray matter. It contains the spinal tracts which ascend and descend the spinal cord.

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what is contained in the subdural space?

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interstitial fluid

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what is contained in the epidural space?

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FAT AND CONNECTIVE TISSUE

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where do you find interneurons and what do they do?

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is a neuron that forms a connection between other neurons. Interneurons are neither motor nor sensory. The term is also applied to brain and spinal cord neurons whose axons connect only with nearby neurons,

Integrative function. The nervous system processes sensory information by analyzing and storing some of it and by making decisions for appropriate responses—an activity known as integration. An important integrative function is perception, the conscious awareness of sensory stimuli. Perception occurs in the brain. Many of the neurons that participate in integration are interneurons [Pronunciation] (neurons that interconnect with other neurons), with axons that extend for only a short distance and contact nearby neurons in the brain or spinal cord to set up the complex “circuit boards” of the central nervous system. The vast majority of neurons in the body are interneurons. These neurons make up the majority of the central nervous system.

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synapses

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For synapses between neurons, the neuron sending the signal is called the presynaptic neuron [Pronunciation] , and the neuron receiving the message is referred to as the postsynaptic neuron (Figure 16.3c). Most synapses between neurons are axodendritic (ak′‐sō‐den‐DRIT‐ik), from presynaptic axon to postsynaptic dendrite, while others are axosomatic (ak′‐sō‐sō‐MAT‐ik), from presynaptic axon to postsynaptic cell body (soma), or axoaxonic (ak′‐sō‐ak‐SON‐ik), from presynaptic axon to postsynaptic axon.
Synapses between neurons may be electrical or chemical. In an electrical synapse, the plasma membranes of the presynaptic and postsynaptic neurons are tightly bound by gap junctions that contain connexons (see Figure 3.2e). As ions flow from one cell to another through the connexons, a nerve impulse is generated and passes from one cell to another. Although electrical synapses are not as common as chemical synapses in the brain, they are quite common in visceral smooth muscles, cardiac muscle tissue, and the developing embryo. Electrical synapses permit very rapid communication and uniform, coordinated movements, such as those required to make the heart beat.

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which way do efferent and afferent pathways send information?

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In the nervous system, afferent neurons (otherwise known as sensory or receptor neurons), carry nerve impulses from receptors or sense organs towards the central nervous system. This term can also be used to describe relative connections between structures. Afferent neurons communicate with specialized interneurons. The opposite activity of direction or flow is efferent.

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the peripherial nervous system is divided into 3 systems

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Somatic
Autonomic
Enteric

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what info do the somatic motor neurons carry?

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Somatic motor neurons, which originate in the central nervous system, project their axons to the target tissues, which are always skeletal muscles.[1] Skeletal muscles are involved in locomotion (such as the muscles of the limbs, abdominal, and intercostal muscles).

convey info from the CNS to skeletal muscles only. Responsible for muscle contraction