Level 2 Unit 2 Part 1: Lower functional neuroanatomy

The lower, or more basic, neural functions are carried out by many parts of both the central and peripheral parts of the nervous system, and include sensory, motor, and autonomic functions.

The nervous system can sense many aspects of the body and the environment. Each type of stimulus that can be sensed is detected by some type of receptor. Most types of sensory information is then transmitted from receptors in the periphery to the central nervous system by afferent axons in the peripheral nervous system. Vision occurs through the eyes, hearing through the ears, smell through the nose, and taste through the mouth. There is a sense from the inner ear called vestibular sense, which involves head movements and the direction of gravity. There are multiple senses of the body collectively called somatosensation, including the senses of touch, position of body parts, vibration, pain, and temperature. Position sense is also called proprioception. Somatosensory stimuli are detected by receptors in the skin and deep tissues. Many types of sensory information travel through chains of neurons to areas of the cerebral cortex for conscious perception, while others are “unconscious”, meaning they travel to other parts of the central nervous system to contribute to other functions without being consciously perceived.

The word motor in this context refers to control of skeletal muscle contraction for movement, tone, and posture. The somas of lower motor neurons are in the brain or spinal cord, and their efferent axons in the peripheral nervous system connect to and control skeletal muscle cells. Upper motor neuron somas are in the central nervous system, mostly in the cerebral cortex, and their axons project through central nervous system tissue to other parts of the brain, or to spinal cord, where they connect to and control lower motor neurons. Several other parts of the brain influence the activity of the upper motor neurons as they control the lower motor neurons, which in turn control skeletal muscle cells. Some motor activities are voluntarily, meaning they are under conscious volitional control, while others are involuntary. An important group of involuntary motor activities are the motor reflexes, which are motor responses to stimuli that do not require conscious involvement. Many motor reflexes involve lower motor neurons responding directly to input from sensory neurons, as opposed to voluntary motor activity where lower motor neurons are controlled by upper motor neurons.

Autonomic functions are a different group of activities do not require the involvement of consciousness, and involve basic physical processes like circulation and digestion. These functions involve autonomic neurons, whose efferent axons in the peripheral nervous system contact and control smooth muscle cells, cardiac muscle cells, and some gland cells. Smooth muscles cells are widespread in many tissues of the body, such as the airways of the lungs and the walls of blood vessels, and often play a major role in how organs function. Cardiac muscle cells make us most of the heart tissue, and contract to push blood through the circulatory system. The autonomic nervous system is divided into two parts called the sympathetic and parasympathetic nervous systems; these usually cause opposite effects on the tissues they influence. Certain areas of the brain connect to and influence the activity of autonomic neurons, shifting the balance of activity between the sympathetic and parasympathetic parts.

Next:

Level 2 Unit 2 Part 2: Higher functional neuroanatomy

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