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Nervous System Part III

Nervous System Part III . Nerve Pathways. Nerve pathways are the routes that nerve impulses take within the nervous system The simplest of these pathways consist of only a few neurons and are called reflex arcs Reflex arcs begin with a receptor on the end of a sensory fiber

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Nervous System Part III

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  1. Nervous System Part III

  2. Nerve Pathways • Nerve pathways are the routes that nerve impulses take within the nervous system • The simplest of these pathways consist of only a few neurons and are called reflex arcs • Reflex arcs begin with a receptor on the end of a sensory fiber • This sensory fiber leads to several interneurons located in the CNS • The interneurons communicate with motor fibers

  3. Reflex Behavior • Reflexes are • Automatic subconscious responses to changes • The help to maintain homeostasis by controlling many involuntary functions such as • Heart rate • Breathing rate • Blood pressure • Digestion • Swallowing • Coughing • Vomiting

  4. Reflex Behavior • Knee-jerk reflex • Simple reflex that involves only two neurons • The sensory axon communicates with a motor neuron within the spinal cord to make the leg move • Helps to maintain upright posture

  5. Reflex Behavior • Withdrawal reflex • Occurs when a person suddenly touches a body part to something painful • Skin receptors send impulses through sensory nerves to the spinal cord • Interneurons of a reflex center within the spinal cord directs motor neurons to send impulses to the appropriate muscle groups • Other impulses are sent to the brain where a person then becomes aware of what is occurring

  6. Meninges • Meninges are layered membranes that protect the soft tissues of the brain and spinal cord from their bony surroundings • Have three layers • Duramatter-outer most layer, composed of tough fibrous connective tissue with lots of blood supply and nerves • Arachnoid matter – thin, web like membrane without blood vessels that lies between the dura matter and pia matter • Pia matter- very thin and contains many nerves and blood vessels that nourish underlying cells of the brain and spinal cord • Brospinal fluid- fluid located between the arachnoid and pia matter

  7. Spinal Cord • Spinal Cord-is a slender nerve column that passes downward from the brain into the vertebral column • Is continuous with brain tissue but technically starts when nervous tissue leaves the skull at the foramen magnum (large hole at the base of the skull) • Ends near the intervertebral disc between the 1st and 2nd lumbar vertebrae

  8. Spinal Cord • Consists of 31 segments each of which give rise to a pair of spinal nerves • Two grooves extend the length of the spinal cord and separate into right and left halves • A cross section of the spinal cord reveals a core of grey matter within white matter • Neurons located in the white matter are largely motor fibers • Neurons located in the grey matter are largely interneurons

  9. Functions of the Spinal Cord • Two major functions • Conducting nerve impulses • Serving as a center for spinal reflexes • The nerve tracts of the spinal cord consist of axons that provide two-way communication between the brain and body parts • The tracts that carry sensory information to the brain are called ascending tracts • The tracts that conduct motor impulses to the muscles and glands are called descending tracts

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