The Nervous System Chapter 35

Maintaining Homeostasis Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in external environments. Homeostasis in the body is maintained by feedback inhibition.

Maintaining Homeostasis Feedback inhibition (negative feedback) = the process in which a stimulus produces a response that opposes the original stimulus.

Maintaining Homeostasis An Example of Feedback Inhibition Thermostat senses temperature change and switches off heating system Room temperature increases Room temperature decreases Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in external environments. A home heating system uses a feedback mechanism to maintain a stable, comfortable environment within a house. Thermostat senses temperature change and switches on heating system

35.2 The Nervous System An Overview The NS interprets stimuli and coordinates other organ systems to respond to stimuli A nerve impulse, or action potential, is an electrical signal that travels like a wave over the length of a nervous system cell called a neuron

Cells of the NS Neurons include: Sensory neurons transmit impulses from the environment to the spinal cord and brain Motor neurons carry instructions from the brain and spinal cord to muscles and glands Interneurons are the most abundant and transmit signals from one neuron to another

Anatomy of a Neuron The cell body contains the nucleus and other organelles Dendrites receive stimuli and conduct impulses towards the cell body The axon carries impulses away from the cell body Cell Body Dendrite Axon

Nodes of Ranvier are the gaps between neighboring Schwann cells Axon Terminals Direction of impulse Nodes of Ranvier Myelin Sheath The myelin sheath is composed of cells called Schwann cells and insulate the axon Nodes of Ranvier are the gaps between neighboring Schwann cells Axon terminals are the ends of the axon

The Synapse A synapse is the space between a neuron and another cell

Neurotransmitters are chemicals that are stored in the axon terminals and released into a synapse when triggered by an impulse send message to the next neuron An impulse begins when a neuron is stimulated by another neuron or by the environment.

35.3 Divisions of the Nervous System 2 Major Divisions: Central Nervous System (CNS) = the brain and spinal cord Peripheral Nervous System (PNS) = cranial and spinal nerves

The CNS The central nervous system relays messages, processes information, and analyzes information. meninges = the protective membrane covering the brain and spinal cord cerebrospinal fluid (CSF) = fluid that circulates around the CNS and provides cushioning entire CNS encased in bone

The Human Brain Cerebrum Thalamus Pineal gland Hypothalamus Cerebellum Pons Pituitary gland Hypothalamus Cerebrum Medulla oblongata Spinal cord Cerebellum Pineal gland Thalamus

Adult human brain is composed of ~100 billion neurons The cerebrum is the largest and most prominent region of the human brain. controls the voluntary, or conscious, activities of the body divided into right and left hemispheres, which control sensory and motor functions of the opposite side of the body

The second largest region of the brain is the cerebellum. coordinates and balances the actions of the muscles so that the body can move gracefully and efficiently The brain stem connects the brain and spinal cord. It has two regions: the pons and the medulla oblongata. Each region regulates information flow between the brain and the rest of the body. Blood pressure, heart rate, breathing, and swallowing are controlled in the brain stem.

The spinal cord is the main communications link between the brain and the rest of the body. certain information, including some kinds of reflexes, are processed directly in the spinal cord. A reflex is a quick, automatic response to a stimulus.

Concept Map The Nervous System Section 35-3 is divided into Central nervous system Peripheral nervous system which consists of which consists of Spinal Nerves Brain Spinal Cord