Unit VII - The Nervous System: Part 1 Nerve Cells & the Central Nervous System

Structural Subdivisions Central NS Brain & Spinal Cord Peripheral NS Cranial & Spinal Nerves

Functional Subdivisions

Functional Subdivisions Somatic NS Information to/from voluntarily controlled organs (skeletal muscles) Somatic Sensory – Information In (afferent) Somatic Motor – Information Out (efferent) Autonomic NS Information to/from involuntary organs (smooth & cardiac muscles and glands) Sympathetic Division – “fight or flight” Parasympathetic Division – “rest & repair”

Divisions of the Autonomic NS “rest & digest” “fight or flight” Divisions of the Autonomic NS

Cells of the Nervous System Two Categories: Neurons – transmit messages Neuroglia – “assistants”

Neuron Structure Cell Body (soma) Resembles other cells; holds organelles Dendrites Highly branched; receive signals Axons Long process; Sends signals out Usually covered in a myelin sheath Larger diameter = faster conduction

Structural Classification of Neurons Bipolar 1 axon; 1 dendrite; (both branched at tips) rare Unipolar 1 process; divides into 1 axon & 1 dendrite (branched at tips) sensory Multipolar 1 axon; several dendrites

Functional Classification of Neurons Afferent (Sensory) Neurons Transmit to spinal cord or brain Efferent (Motor) Neurons Transmit to muscles and glands Interneurons Conduct between sensory and motor neurons synapse = where neurons meet other neurons, muscles, or glands

The Other Cells of the NS… Glia (Neuroglia) – “nerve glue” Do not conduct information Serve as support Numerous! Able to reproduce

Types of Glia Astrocytes Largest & most common glia cells Transfers nutrients from blood to neurons Forms the blood-brain barrier Astro = star

Types of Glia Microglia Smallest glial cells Phagocytize (eat) when brain inflamed Micro = small Glia = glue

Types of Glia Ependymal Cells Form sheets that line fluid-filled areas Help form fluid and help move it (cilia) Hint: think of cilia like apPENDages

Types of Glia Oligodendrocytes Few branches Make the myelin sheath around nerves in CNS Help hold nerve fibers together Oligo = few Dendr = tree (branches)

Types of Glia Schwann Cells Only in peripheral NS (nerves) Forms myelin sheath

Synapses Site where axon of one neuron meets with a neuron, a muscle cell, or a gland cell

Synapses Vesicles receive signal to secrete neurotransmitter which travels across synaptic cleft (space) and eventually binds to receptors on the post-synaptic cell (the next cell). This carries the activation signal to that next cell.

Neurotransmitters Acetylcholine Serotonin Dopamine Epinephrine Excites skeletal muscle Serotonin Moods; emotions; sleep Dopamine Emotions; mood; motor control Epinephrine Fight or flight

Side Note: Drugs & Neurotransmitters Some drugs (like cocaine) block the re-uptake of dopamine This causes too much dopamine to signal next cell In the case of cocaine, this causes over-stimulation of pleasure center in brain Long-term effect though, is that body stops making enough dopamine

Side Note: Drugs & Neurotransmitters Some toxins work by blocking enzymes that break down acetylcholine (ACh) ACh never leaves receptor - nerve impulse cannot fire anymore, so muscles can not contract

Reflex Arcs stimulus -> sensory neuron -> CNS -> interneuron -> motor neuron -> effector

Nerves Bundles of fibers of peripheral NS Nerve cell - bound by endoneurium Fascicle - bound by perineurium Complete nerve - bound by epineurium

Nerves Nerve bundles with myelin sheaths look white Bundles without myelin sheaths look gray

Nerve Repair Mature neurons cannot do mitosis, so cannot be replaced Neurons in PNS might be repaired, but cannot do so very well Distal part of axon degenerates “sprouts” of axon appear & move to broken spot to connect In CNS, repair is very unlikely

Types of Nerve Damage

The End

FAKE QUIZ! Answer in your notebook – on a left-side page if possible. You do not need to write the questions, but you may want to do so for study purposes.

Self Quiz 1. Fill in the blanks… Nervous System Structural Divisions Functional Divisions __A__ __B__ __C__ __D__ Brain & __E___ Afferent __F___ __G___ Spinal Cord (Sensory) Parasympathetic

Self Quiz 1. Fill in the blanks… Nervous System Structural Divisions Functional Divisions CNS PNS Somatic Autonomic Brain & Nerves Afferent Efferent Sympathetic Spinal Cord (Sensory) (Motor) Parasympathetic

Self Quiz Match the nervous system cells with the appropriate descriptions… A. oligodendrocytes C. astrocytes E. microglia B. ependymal cells D. Schwann cells F. neurons Connect the neurons to capillaries The two types that form myelin sheaths Engulf (eat) debris surrounding damaged nervous tissue Transmit electrical messages 6. Allow for better movement of cerebrospinal fluid

Self Quiz Match the nervous system cells with the appropriate descriptions… A. oligodendrocytes C. astrocytes E. microglia B. ependymal cells D. Schwann cells F. neurons Connect the neurons to capillaries - C The two types that form myelin sheaths – A & D Engulf (eat) debris surrounding damaged nervous tissue - E Transmit electrical messages - F 6. Allow for better movement of cerebrospinal fluid - B

Self Quiz 7. Label the parts… A (wraps nerve) B (bundle of cells) C (wraps cell) Nerve Cell

Self Quiz 7. Label the parts… A - epineurium B - fascicle C - endoneurium Nerve Cell

Self Quiz 8. Name the parts of the neuron… axon - soma/cell body – dendrite - myelin sheath A B C D

Self Quiz 8. Name the parts of the neuron… axon - soma/cell body – dendrite - myelin sheath A - dendrites B – myelin sheath C - axon D – soma/cell body