Notes Ch. 11D Nervous System II Anatomy and Physiology

Spinal Cord The spinal cord is a slender column of nervous tissue that is connected to the brain and extends down through the vertebral canal.

Structure of the Spinal Cord The spinal cord is made of thirty-one segments, each segment has a pair of spinal nerves attached. These branch to various body parts. There are 2 grooves that are along the length of the spinal cord that divides it into left and right halves. The cord is white matter surrounded by gray matter.

Functions of the Spinal Cord There are 2 main functions of the spinal cord. It is a center for spinal reflexes and it is a way to send impulses to and from the brain.

Reflex Arcs A nerve pathway is 2 or more neurons involved in communication. The simplest nerve pathway starts with a sensory receptor and ends with an effector. This is called a reflex. The parts of a reflex is called a reflex arc. This starts with a sensory receptor, enters the CNS and is processed and then moves from the CNS to effectors.

Reflex Behavior Reflexes and automatic responses to changes inside or outside the body. They help keep homeostasis in check by controlling heart rate, breathing rate, blood pressure, and digestion. Reflexes are also important for swallowing, sneezing, coughing, and vomiting. T

he patellar reflex (knee-jerk reflex) is an example of a monosynaptic reflex. It only uses 2 neurons. This reflex helps keep the body upright posture. Another reflex is the withdrawal reflex. This is when a person touches something painful and they pull away from it. (you can read more about each reflex on pg. 412- 413)

Ascending and Descending Tracts Spinal tracts that move sensory information to the brain are called ascending tracts. Tracts that move information from the brain to motor neurons to muscles and glands are called descending tracts.

Ascending pathways Ascending pathways usually have 3 neurons between a sensory receptor and the final destination. Fasciculus gracilis and fasciculus cuneatus - they move sensory impulses from the skin, muscles, tendons, and joints to the brain. They are interpreted as touch, pressure, and body movement. 2. Spinothalamic tracts move impulses from body regions to the brain and they give pain and temperature perception. 3. Spinocerebellar tracts move impulses from the muscles of the lower limbs and trunk to the brain. They coordinate muscular movements.

Descending Pathways Corticospinal tracts - These move motor impulses from the brain to lower motor neurons and into skeletal muscles. They carry information to control voluntary movements. Reticulospinal tracts move motor impulses from the brain and control muscle tone and sweat glands. 3. Rubrospinal tracts move impulses from the brain to help coordinate muscle actions.