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The Nervous System. The Nervous System Page 897. The nervous system is an intricate communication network that coordinates and controls functions throughout the body, responding to internal and external stimuli. .
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The Nervous System Page 897 • The nervous system is an intricate communication network that coordinates and controls functions throughout the body, responding to internal and external stimuli.
Tiny jolts of energy called impulses travel along this network at tremendous speeds. (243 mph recorded between cells.)
Messages travel over many routes carrying information about both the external environment and the internal environment.
All vertebrates have a nervous system (NS) made up of a: - central nervous system (CNS) and a - peripheral nervous system (PNS).
Central nervous system (CNS) • CNS: - consists of nerves of the brain and the spinal cord. • coordination center for ingoing and outgoing information.
- covered by three protective membranes. These membranes are called the meninges. (With meningitis, these membranes swell.)
- Between the inner two layers is a clear fluid called cerebrospinal fluid which: - absorbs shock - transfers nutrients to the brain - removes wastes from the brain
CNS is composed of: a. Brain: - control center - covered in grey matter (cerebral cortex) which has many deep folds in it called fissures. (These increase the surface area.) - also protected by skull
The Brain • There are over 100 billion nerve cells in the brain.
b. Spinal cord: - carries sensory messages from receptors to the brain and motor messages from brain to muscles and glands - also controls many reflex responses - white matter on the outside; grey on the inside - protected by the vertebrae
Parts of the brain • Cerebrum (p. 902): - largest and most highly developed - intelligence, thinking, creativity, reasoning, memory - voluntary activities of the body
Each hemisphere has 4 lobes: • Frontal lobe: controls speech, motor activities (muscles), learning, judgement, creativity, organization • Parietal lobe: perception, recognition, touch, temperature, memory • Occipital lobe: vision, interpretation • Temporal lobe: senses (smell, taste, hearing), some memory
THE CEREBRUM IS ALSO DIVIDED INTO TWO LAYERS: • Outer, cerebral cortex, gray matter which consists of tightly packed nerve cell bodies. • Inner, white matter, consists of bundles of axons with myelin sheaths. • Connects the cerebral cortex and the brain stem.
The cerebrum is divided into two hemispheres (right and left, each controlling and receiving information from the opposite side of the body)
Corpus callosum: - Connects the two hemispheres • Brain stem: - Consists of the medulla oblongata, ponsVarolii, and midbrain, that connect the spinal cord to the cerebrum.
Pons: • Bridge between the cerebrum and the cerebellum • Cerebellum: • Balance, muscle tone • Medulla Oblongata • Involuntary muscles • Internal organs • Heart rate, respiration
Thalamus: -Part of the brain that lies just below the cerebrum - Acts as a relay station by receiving impulses from most of the sensory neurons and directing these impulses to the part of the brain where each will be interpreted. -Screens out less significant stimuli (prevents sensory overload)
Hypothalamus: • Coordinates NS and endocrine system
The Spinal Cord • Carries thousands of messages at once • Main communication link between brain and the rest of the body • Thirty-one pairs of spinal nerves branch out from the spinal cord • Certain kinds of information, including some reflexes, are processed directly in the spinal cord.
Peripheral Nervous System • Consists of all the nerves and associated cells which are not part of the central nervous system. • Is divided into the: • Sensory division: transmits impulses from sense organs to the CNS • Motor division: transmits impulses from the CNS to the muscles or glands.
Somatic and Autonomic Nervous Systems The motor division is further divided into the somatic nervous system and the autonomic nervous system.
The somatic nervous system regulates activities that are under conscious control (ie. the movement of the skeletal muscles) (Some somatic nerves are also involved with reflexes and can act without conscious control.)
Autonomic Nervous System • The autonomic nervous system regulates body activities that are automatic or involuntary. (ex. When a person is running, the autonomic nervous system speeds up heart rate and blood flow, stimulates sweat and adrenal glands, and slows down the contractions of the smooth muscles of the digestive system.)
The autonomic nervous system is further subdivided into two parts: • sympathetic nervous system • parasympathetic nervous system which have opposite effects on the same organ system. (Think gas and brake when driving a car.) (Sympathetic nervous system speeds up heart rate; parasympathetic slows it down.)
Neurons • The messages carried by the nervous system are called impulses. • Neurons, (nerve cells) are classified into three types, depending on the direction the nerve impulse travels along them: • Sensory neurons - sense organs (receptors) to spinal cord and brain • Motor neurons – brain and spinal cord to muscles and glands • Interneurons connect sensory and motor neurons and carry impulses between the two of them
All organisms respond to changes in their environment. A reaction to stimulus is called a response. • A stimulus is a change in the environment that induces a response. These stimuli are received through specialized sensory receptors usually found on the nerve endings.
The parts of the body that respond to messages from the brain and spinal column are called effectors.
Understanding a nerve impulse • A neuron that is not transmitting a nerve impulse has a net negative charge inside and a net positive charge on the outside. • When not transmitting an impulse, the selectively permeable cell membrane allows potassium
