CHAPTER SEVENTEEN
Answers to WHAT DID YOU LEARN?
1.
In decussation, an axon crosses over to the opposite side of the CNS somewhere
along its length. Thus, sensory information from the right side of the body is
processed by the left side of the brain, and vice versa.
2.
Sensory pathways conduct information related to limb position, touch,
temperature, pressure, and pain.
3.
The primary neuron is the first neuron in the three-neuron chain. It is a sensory
neuron whose dendritic endings house the receptors that detect a specific
stimulus. The cell bodies of primary neurons reside in the posterior root ganglia
of spinal nerves. The secondary neuron is the second neuron in the three-neuron
chain. It is an interneuron, and its cell body resides within either the posterior
horn of the spinal cord (if the primary neuron is associated with a spinal nerve) or
within one of the brainstem nuclei (if the primary neuron is associated with a
cranial nerve).
4.
The posterior funiculus-medial lemniscal pathway conducts proprioceptive
information concerning limb position. The spinocerebellar pathways conduct
proprioceptive information about joints, skeletal muscles, and tendons.
5.
Four separate CNS components form the somatic motor pathways: cerebral
nuclei, the cerebellum, descending pathways, and motor neurons and
interneurons.
6.
The cell body of an upper motor neuron is housed within either the cerebral cortex
or a nucleus within the brainstem. Axons of the upper motor neuron synapse
either on lower motor neurons or on interneurons. The cell body of a lower motor
neuron is housed either within the anterior horn of the spinal cord or within a
brainstem cranial nerve nucleus. Axons of the lower motor neurons exit the CNS
and project to the skeletal muscle to be innervated.
7.
A direct motor pathway (also called the pyramidal pathway) originates in the
pyramidal cells of the primary motor cortex. This type of pathway is involved in
the conscious control of movements. Midbrain nuclei initiate motor commands
for the indirect motor pathways. They work at an unconscious level to control
movements.
8.
Cerebral nuclei do not exert direct control over lower motor neurons; instead, they
adjust the motor commands issued in other nuclei and provide a background
pattern and rhythm once a movement is under way. The cerebral nuclei also play
a key role in cognition and in emotions. The cerebellum influences and controls
movement by indirectly affecting the excitability of motor neurons through its
actions on the descending motor pathways. The cerebellum is critically important
in coordinating movements by specifying the precise timing of control signals to
different muscles.
9.
Wernicke’s area is an analytical area housed within one hemisphere, usually
the left. This area is involved in interpreting written and spoken language.
10.
11.
12.
The left hemisphere is usually called the categorical hemisphere. The left
hemisphere contains the general interpretive and speech centers, and is
specialized for language abilities as well as analytical and reasoning tasks.
The other hemisphere, usually the right, is called the representational
hemisphere, because it is concerned with spatial relationships. It relates the
body to the sensory environment and is the seat of imagination and insight,
musical and artistic skill, and comparison of sights, sounds, smells, and tastes.
Mental processes such as awareness, knowledge, memory, perception, and
thinking are collectively called cognition.
Encoding is the process of organizing information in STM before it is
consolidated into LTM.