Chapter 33 Notes, The Nervous System

Nervous System A neuron is a cell of the nervous system that carries nerve impulses through the body. There are three kinds of neurons in the body. Interneurons are neurons that are found in the brain and the spinal cord. Interneurons process information received from the sensory neurons, and transmit that information to motor neurons.

Nervous System Sensory neurons send information to the interneurons and they are found mostly in the skin, but they are also connected to organs. Motor neurons receive information from the interneurons to produce a response in the muscles and glands.

Neurons

The Nervous System The nervous system consists of two divisions. The central nervous system (CNS) includes the interneurons of the brain and spinal cord. The peripheral nervous system consists of the sensory neurons and motor neurons that carry information to and from the CNS.

The Central and Peripheral Nervous Systems

Reflexes Sometimes an impulse triggers an involuntary reflex that does not involve the brain. The sensory neurons send information to the spinal cord, and the spinal cord sends information directly back to a motor neuron without processing the information in the brain. This is known as a reflex arc.

(Patellar Reflex) Reflex Arc

The Brain The largest part of the brain is called the cerebrum. It is divided into two halves called the cerebral hemispheres. The cerebrum is responsible for learning, memory, language, speech, voluntary body movements and sensory perception. The many folds and grooves on the surface of the cerebrum increase surface area and allow more complicated thought processes.

The Cerebrum

The Brain The next largest part of the brain, located near the back of the brain, is called the cerebellum. The cerebellum is responsible for balance, posture, and coordination. The brain stem connects the brain to the spinal cord. The brain stem is made up of two parts; the medulla oblongata and the pons. The medulla oblongata relays signals between the brain and the spinal cord, and it controls the breathing rate, heart rate, and blood pressure.

Cerebellum, Medulla Oblongata, and the Pons

The Brain The pons relays information between the cerebrum and the cerebellum. A small region of the brain called the hypothalamus maintains homeostasis. The hypothalamus maintains body temperature, thirst, appetite, and water balance. Additionally, the hypothalamus regulates sleep, and some emotions like aggression, and fear.

The Hypothalamus

The Nervous System The Peripheral Nervous System can be divided into two subdivisions. The two subdivisions are called the Somatic Nervous System and the Autonomic Nervous System. Neurons of the body that are under voluntary control, and use skeletal muscles are part of the somatic nervous system. However, a reflex arc is also an involuntary response of the somatic nervous system.

The Nervous System The part of the nervous system that controls the internal organs, and that are under involuntary control is called the autonomic nervous system. If you ever came close to running into a moose while driving, or if you were ever involved in a car accident, you probably felt your body's fight-or-flight response. Your internal organs are controlled by the autonomic nervous system. Your fight-or-flight response is also controlled by the autonomic nervous system.

Organization of the Nervous System

The Nervous System The autonomic nervous system also has two subdivisions; they are called the sympathetic and parasympathetic nervous system. The sympathetic nervous system is most active in times of emergency or stress. The heart rate and breathing rate is elevated, pupils dilated. The parasympathetic nervous system is most active when the body is relaxed.

Sympathetic vs. Parasympathetic Nervous System

The Sensory Organs A region of the brain that has special sensory neurons responsible for the sense of smell is called the olfactory bulb. The nerves of the olfactory bulb are called olfactory nerves. Areas of chemical receptors on the tongue responsible for taste are called taste buds. The olfactory nerves and taste buds communicate with one another to enhance the flavor of food. Without smell, food loses flavor.

Taste and Smell

Taste and Smell

The Sensory Organs When light enters the eye it first travels through a transparent layer of cells called the cornea. The amount of light entering the eye is controlled by muscles of the iris, which is the part of the eye that is colored. Behind the iris is the lens. The lens inverts the image and projects it onto the retina. The retina contains cells called rods and cones. Rods help to see in low-light. Cones function in bright light and detect color.

Anatomy of the Eye

The Sensory Organs The two functions of the ear are hearing and balance. Sound waves enter the auditory or ear canal. Sound waves cause the eardrum or tympanum to vibrate. These vibrations cause three bones in the middle ear called the malleus (hammer), incus (anvil), and stapes (stirrup) to vibrate. Vibrations from these bones cause fluid inside the cochlea to move tiny hairs. These tiny hairs send nerve impulses to the brain that interpret sounds generated by sound waves.

Anatomy of the Ear

The Sensory Organs Inside the inner ear, located near the cochlea are three canals called semicircular canals. The semicircular canals are also filled with fluid and tiny hairs. These hairs in the canals are responsible for balance. As you move, the fluid in the canals causes the hairs to bend in response to gravity and motion. These hairs sends signals to the brain that allow us to achieve balance and equilibrium.

Anatomy of the Ear