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Divisions of the Nervous System Unit 8: Human Body Systems Chapter 35-3 Divisions of the Nervous System • 2 major divisions: Central Nervous System Brain Spinal Cord Nervous System Peripheral Nervous System Nerve cells Central Nervous System (CNS) A. The Central Nervous System (CNS) • Control center of the body • Relays messages, processes & analyzes information • Made of two parts: – Brain – Spinal cord • 1. The Brain – Impulses flow to and from the brain – 100 billion neurons, mainly interneurons • 2. Spinal Cord – Main communication link between brain and the rest of the body – Processes information such as reflexes 1. Protection of the CNS • Brain and spinal cord are protected by: • a) Bone – skull and vertebrae • b) Meninges – 3 layers of connective tissue that surround the organs • Dura mater—outer covering of brain and spinal cord • Arachnoid—middle layer • Pia mater—inner covering of the brain and spinal cavity • c) Cerebrospinal fluid – fluid found in between meninges and organ – Acts as a shock absorber – Continually circulates around the brain 2. Regions of the Brain • Regions of the Brain – Cerebral hemispheres (Left & Right) – Diencephalon – Brain stem – Cerebellum a. Cerebral Hemispheres (Cerebrum) • Left and right hemispheres – Left brain – logic, language, math – Right brain – creativity • Connected by the corpus callosum (communication link between right and left) • The surface is made of ridges (gyri) and grooves (sulci) Fissures (deep grooves) divide the cerebrum into four lobes 1. Occipital Lobe: visual integration 2. Parietal: spatial knowledge, math 3. Temporal: memories, auditory, language 4. Frontal: emotion, future planning, judgment, muscle movements, language • Limbic System – involved in emotion, motivation, arousal, memory, and learning – Amygdala – fear – Hippocampus – memory formation b. Diencephalon • Relay and control center • Sits on top of brain stem • Two main parts: – 1) Thalamus – relay between sensory areas and cerebrum – 2) Hypothalumus – regulates involuntary responses & hormone secretions of the pituitary gland c. Brain Stem • Attaches brain to spinal cord • Parts of the brain stem – Midbrain – vision, hearing, motor control – Pons – breathing, sleep – Medulla oblongata involuntary activities (breathing, heart rate, blood pressure) d. Cerebellum • “Little brain” inferior to and posterior to cerebral cortex • Coordination, posture, motor learning 3. Spinal Cord • Cylinder of nervous tissue that begins at base of brain • Protected by the vertebral column and meninges • Spinal nerves extend from the cord through each vertebrae • Main communication link between brain and the body Peripheral Nervous System (PNS) Peripheral Nervous System (PNS) Sensory Division Motor Division Somatic NS Autonomic NS Sympathetic Parasympathetic B. Peripheral Nervous System (PNS) • Peripheral Nervous System is made up of all the nerves and ganglia (nerve cell bodies) that carry messages between the body and the CNS • Receives info from the environment • Transmits commands from CNS to organs and glands • Contains mostly motor and sensory neurons Divisions of the PNS • Sensory division • Motor division – transmits – transmits impulses from impulses from sense organs to the central the central nervous system nervous system to the muscles or glands – Divided into 2 divisions • Somatic • Autonomic Motor Division • Somatic N.S. • Autonomic N.S. • Regulates activities that are under conscious control • Example: movement of muscles (wiggle toe) • Involved in reflexes (quick, automatic response to stimulus) • Regulates activities that are automatic or involuntary • Example: heart rate • Consists of only motor nerves • Divided into two divisions – Sympathetic division – Parasympathetic division Autonomic N.S. Division • Sympathetic • Parasympathetic • “Fight-or-Flight” • Takes over to increase activities • Remember as the “E” division = exercise, excitement, emergency, and embarrassment • “Rest and Digest • Conserves energy • Maintains daily necessary body functions • Remember as the “D” division = digestion, defecation, and diuresis (urination) Peripheral Nervous System & Reflexes • The peripheral nervous system is also involved in reflexes. • A reflex is a quick and unconscious response to a stimulus • The brain is not involved with reflexes. The Nervous System CNS Brain Spinal Cord PNS Somatic NS Voluntary Movement Autonomic NS Involuntary Movement Sympathetic Parasympathetic NS NS fight or flight rest & digest