NASM CHAPTER 2: THE NERVOUS SYSTEM

Central Nervous System

Consists of the brain and the spinal cord, and its primary function is to coordinate the activity of all parts of the body.

Neuron

Functional unit of the nervous system. Billions of neurons make up nervous system, provides it with ability to communicate internally with itself as well as externally with environment. Transmits impulses through both electrical and chemical signals. Forms the core of the nervous system which includes the brain, spinal cord, and peripheral ganglia. Neurons are composed of cell body, axon, and dendrites. The cell body of Neuron contains a nucleus, lysosomes, mitochondria, and a Golgi complex.

Peripheral Nervous System

Nerves that connect the CNS to the rest of the body and the external environment. Nerves of PNS are how CNS receives sensory input(from sensory afferent neurons) and initiates responses(through motor efferent neurons). The PNS serve two main functions. They provide a connection for the nervous system to activate different effector(organ, muscle) sites. Second they relay information from effector(organ, muscle) sites back to the brain via sensory receptors, providing constant update to the relation of the body and the environment. The PNS consists of the somatic and autonomic nervous system. The somatic nervous system consists of the nerves that serve the outer areas of the body and skeletal muscle and are responsible for the voluntary control of movement. So somatic is what controls your biceps and legs and whatnot. The autonomic nervious system supplies neural input to the involuntary systems of the body, like your heart. Autonomic, auto, think autopilot, you don't have conscious control over the autonomic process. The autonomic is divided into sympathetic and parasympathetic nervous systems. The sympathetic system increases the activation level of neurons in preparation for activity(ramps you up). The parasympathetic ramps your system down, decreases levels of activation. Sensory receptors are specialized structures that convert environmental stimuli(heat, sound, taste, etc) into sensory information for the brain. These receptors are divided into four categories, mechanoreceptors, nociceptors, chemoreceptors, and photoreceptors.

Sensory (afferent) neurons

Respond to touch, sound, light, and other stimuli and transmit nerve impulses from effector sites(muscles, organs) to the brain and spinal cord.

Muscle Spindles

Sensory receptors, run parallel to muscle fibers. Are sensitive to changes in muscle length and rate of length change. Help regulate the contraction of muscles via the stretch reflex mechanism. This mechanism is a normal response to the body to a stretch stimulus in the muscle, it is designed to protect and prevent overstretching and muscle damage.

Gogli Tendon Organs (GTOs)

Specialized sensory receptors located where the skeletal muscle fibers attach to the tendons. Sensitive to changes in muscular tension and rate of tension change. Activiating the Gogli tendon organ causes the muscle to relax which prevents the muscle from excessive stress or injury.

Interneurons

Transmit nerve impulses from one neuron to another. Hence INTER neuron. Between neurons.

Axon

cylendrical projection from the cell body that transmits nervous impulses to other neurons or effector sites(muscles, organs). Provides communication from brain and spinal cord to other parts of the body.

Dendrites

gather information from other structures and transmit it back into the neuron.

Joint receptors

located around joint capsule, respond to pressure, acceleration, and deceleration of the joint. Signals extreme joint positions and thus helps prevent injury. Performance increases in early stages of training result from changes in the way the CNS controls and coordinates movement. Unsuccesful performances can be cross referenced with other sensory input and new movement strategys found. Regular training causes adapations int he CNS, allowing greater control of movements, thus causing movements to be more smooth and more accurate - improving performance.

Mechanoreceptors

specialized structures that respond to mechanical pressure within tissues and then transmit signals through sensory nerves. Respond to outside forces such as touch, pressure, stretching, sound waves, and motion. Senses distortions in body tissues.

Motor (efferent) neurons

transmit nerve impulses from the brain and spinal cord to the effector sites such as muscles or glands. So sensory neurons transmit from muscles and organs to the CNS. Motor neurons transmit nerve impulses from CNS to muscles and organs. Interneurons transmit impulses between neurons.