THE NERVOUS SYSTEM Regents Biology

KEY WORDS axon cell body dendrite effector interneuron motor neuron OBJECTIVES Upon completion of this unit students will be able to: 1. Explain the functions of a nervous system and describe its basic types of structures. 2. Describe the neuron’s structure and the function of its parts. 3. Name different types of nerves and describe their functions. 4. List the changes that occur as an impulse travels along an axon. 5. Differentiate and give examples of effectors and receptors. 6. Compare and contrast the nervous responses/systems of different organisms. 7. Name the major parts of the brain. 8. Differentiate the CNS and the PNS. 9. Differentiate the autonomic nervous systems and the somatic nervous systems. 10. Describe a reflex arc and the all-or-none response. KEY WORDS axon cell body dendrite effector interneuron motor neuron receptor reflex arc sensory neuron stimulus

THE NERVOUS SYSTEM I. INTRODUCTION Why regulate? To deal with changes in the INTERNAL and EXTERNAL environment To maintain HOMEOSTASIS (stable internal environment) Responses to changes must be REGULATED (controlled and directed) and COORDINATED (occur in the right order or relationship) More complex organisms use the NERVOUS and ENDOCRINE systems for regulation and coordination

A. Protozoans Ameoba and paramecium do not have a nervous system but they do respond to stimuli from the environment. They move toward or away from stimuli. There are two types of taxis: CHEMOTAXIS AND PHOTOTAXIS B. Hydra This group does not have a central nervous system but does have a NERVE NET to receive stimuli from the environment.

C. Earthworm This group has a CENTRAL nervous system which consists of a brain (ganglia) and a VENTRAL nerve cord. Possessing a “CNS” allows directed responses to stimuli. The ventral nerve cord is a characteristic of INVERTEBRATES that have a nervous system.

D. Grasshopper Similar to that of the earthworm in that they also have a VENTRAL nerve cord and a BRAIN at one end of the body; the ANTERIOR end. In addition, more highly developed sensory abilities are illustrated by the development of the compound eyes and the ability to fly.

E. Human The nervous system consists of the Central and Peripheral Nervous Systems. The Central Nervous System (CNS) consists of the BRAIN and the SPINAL CORD The three major divisions of the brain and their functions are: DIVISION OF BRAIN FUNCTION CEREBRUM CONTROLS CONSCIOUS ACTS, PAIN AND OTHER SENSATIONS, THINKING, AND MEMORY CONTROL CEREBELLUM CONTROLS MUSCULAR COORDINATION AND BALANCE MEDULLA CONTROLS INVOLUNTARY ACTS LIKE BREATHING, HEARTBEAT, PERISTALSIS, AND BLOOD PRESSURE

Some other areas of the brain are the hypothalamus and the thalamus The SPINAL CORD lies within and is protected by the vertebrae of the spinal and has two functions: Connects the PNS to the brain Coordinates certain REFLEXES Impulses from sensory neurons travel up the spinal cord to the BRAIN and impulses from the brain are transmitted down through the spinal cord to MOTOR neurons. These impulses travel through peripheral nerves to the MUSCLES and GLANDS

THALAMUS CEREBRUM HYPOTHALAMUS PONS MEDULLA CEREBELLUM SPINAL CORD

2. The Peripheral Nervous System (PNS) includes the neurons which are outside the brain and spinal cord. The neurons connected to the brain are called CRANIAL nerves and the neurons which connect to the spinal cord are called SPINAL nerves. In terms of function, the PNS is divided into two systems, the SOMATIC and AUTONOMIC nervous systems. The SOMATIC Nervous System includes both sensory and motor neurons which connect the central nervous system to skeletal muscles. It is this system which controls VOLUNTARY movement. The AUTONOMIC Nervous System includes the Sympathetic and Parasympathetic systems. These motor neurons regulate many of the INVOLUNTARY activities in the body (heart rate, peristalsis, gland secretions, etc.). The SYMPATHETIC and PARASYMPATHETIC systems are opposite each other in function. If the sympathetic speeds up heart rate, the parasympathetic SLOWS it down to normal rate.

       a) The Sympathetic Nervous System does about the same as the hormone adrenaline. It gets the body ready for action (e.g., emergencies) by releasing the neurotransmitter NOREPINEPHRINE which speeds up heart rate, slows peristalsis, relaxes the bladder, dilates the bronchi and pupil, and constricts blood vessels b) The Parasympathetic Nervous System does the opposite. It brings the body back to normal by releasing the neurotransmitter ACETYLCHOLINE which slows down heart rate, speeds up peristalsis, constricts the bladder, constricts the bronchi and pupil, and dilates blood vessels.

A. Mechanisms of Nervous Regulation II. STRUCTURAL UNITS OF THE HUMAN NERVOUS SYSTEM A. Mechanisms of Nervous Regulation 1.  Receptors – SENSE ORGANS (SKIN, ETC.) RECEIVE THE STIMULUS THAT IS SENT THROUGH THE NEURON 2.  Nerve Cell (NEURON) 3.  Effector – WHERE IMPULSES END UP (TARGET) a.   Gland - INCREASE OR DECREASE SECRETION b.  Muscle – CONTRACT OR RELAX

Three types of neurons 1. SENSORY (a.k.a. afferent) neurons transmit impulses from sense organs (receptors, like the skin) to the CNS. 2. MOTOR (a.k.a. efferent) neurons transmit impulses away from the CNS to the effectors (muscles or glands) 3. INTERNEURON (a.k.a. associative or connector) neurons interpret and relay impulses between sensory and motor neurons. Impulses also originate here (in the brain or spinal cord).

Organization NERVE: bundles of neurons that usually transmit impulses very long distances 2. GANGLIA: enlarged structures which contain interneurons which serve to relay impulses.

D. Structure of an Individual Neuron (nerve cell) CELL BODY NUCLEUS DENDRITES TERMINAL BRANCHES AXON NODE OF RANVIER SCHWANN CELL NUCLEUS MYELIN SHEATH SCHWANN CELL SYNAPTIC KNOBS

E. Reflex Arc: The basic pathway of impulses from stimulus to response

All-or-none Response The all-or-none-response states that EITHER AN IMPULSE IS TRIGGERED OR NOT, DEPENDING ONLY ON WHETHER THE STIMULUS IS ABOVE OR BELOW THE THRESHOLD LEVEL (LIKE FIRING A GUN)