The Peripheral Nervous System UNIT B Chapter 12: Nervous System Section 12.4 The Peripheral Nervous System Connection between the central nervous system and the rest of the body. Contains the Motor and Sensory pathways. peripheral nervous system (PNS): lies outside the central nervous system and is composed of nerves and ganglia TO PREVIOUS SLIDE

Cranial nerves –12 pairs UNIT B Chapter 12: Nervous System Section 12.4 Cranial nerves –12 pairs Largely concerned with the head, neck, and facial regions Vagus nerve (X) branches to internal organs cranial nerves: nerves that arise from the brain Here is the ventral surface of the brain showing the attachment of the 12 pairs of cranial nerves. TO PREVIOUS SLIDE

Spinal Nerves – 31 pairs UNIT B mix of motor and sensory fibres Chapter 12: Nervous System Section 12.4 Spinal Nerves – 31 pairs mix of motor and sensory fibres Dorsal root: sensory fibres that conduct impulses to spinal cord Dorsal root ganglion: cell bodies of sensory neurons Ventral root: motor fibres that conduct impulses away from spinal cord to effectors. Each spinal nerve serves a region of the body in which it is located spinal nerves: nerves that arise from the spinal cord dorsal root ganglia: structures that house the cell body of a sensory neuron Figure 12.12 Cranial and spinal nerves. b. Cross section of the spinal cord showing three pairs of spinal nerves. The human body has 31 pairs of spinal nerves altogether, and each spinal nerve has a dorsal root and a ventral root attached to the spinal cord. TO PREVIOUS SLIDE

Somatic System – Voluntary and Involuntary UNIT B Chapter 12: Nervous System Section 12.4 Somatic System – Voluntary and Involuntary Voluntary - takes sensory information from external sensory receptors to the CNS and motor commands away from the CNS to skeletal muscles Serves the skin, skeletal muscles, and tendons Involuntary - Some actions are due to reflex actions (automatic responses to a stimulus) Sensory Stimuli CNS motor command  skeletal musc Voluntary and involuntary (reflex) somatic system: a subdivision of the peripheral nervous system that serves the skin, skeletal muscles, and tendons The brain is always involved in voluntary muscle actions but somatic system reflexes are automatic and may not require involvement of the brain. reflex actions: automatic responses to a stimulus TO PREVIOUS SLIDE

A spinal nerve reflex arc A stimulus (e.g., a pinprick) causes sensory receptors in the skin to generate nerve impulses that travel in sensory axons to the spinal cord. Interneurons integrate data from sensory neurons and then relay signals to motor neurons. Motor axons convey nerve impulses from the spinal cord to a skeletal muscle, which contracts. Movement of the hand away from the pin is the response to the stimulus.

The Reflex Arc – Reflex involving only Spinal Cord UNIT B Chapter 12: Nervous System Section 12.4 The Reflex Arc – Reflex involving only Spinal Cord Example: withdrawal reflex when touching a sharp object: sensory receptors impulse to interneurons in the spinal cord interneurons signal motor neurons  impulses to skeletal muscle contracts, giving the response to the stimulus. Pain is not felt until the brain receives nerve impulses. Reflexes are built-in circuits that allow for protection and survival TO PREVIOUS SLIDE

UNIT B Chapter 12: Nervous System Section 12.4 Figure 12.13 A somatic reflex arc showing the path of a spinal reflex. A stimulus (for example, a sharp pin) causes sensory receptors in the skin to generate nerve impulses that travel in sensory axons to the spinal cord. Interneurons integrate data from sensory neurons and then relay signals to motor axons. Motor axons convey nerve impulses from the spinal cord to a sketetal muscle, which contracts. Movement of the hand away from the pin is the response to the stimulus. TO PREVIOUS SLIDE

Autonomic System UNIT B Chapter 12: Nervous System Section 12.4 Autonomic System The autonomic system of the PNS regulates the activity of cardiac and smooth muscle, and glands. autonomic system: part of the peripheral nervous system that regulates the activity of cardiac and smooth muscle, and glands TO PREVIOUS SLIDE

Autonomic Nervous System is divided into UNIT B Chapter 12: Nervous System Section 12.4 Autonomic Nervous System is divided into Sympathetic and Parasympathetic divisions. Both function automatically Innervate all internal organs For each signal, they use two motor neurons that synapse at one ganglion Involved in reflex actions such as blood pressure and breathing rate TO PREVIOUS SLIDE

UNIT B Chapter 12: Nervous System Section 12.4 Figure 12.14 Autonomic system structure and function. Sympathetic preganglionic fibres (left) arise from the cervical, thoracic, and lumbar portions of the spinal cord. Parasympathetic preganglionic fibres (right) arise from the cranial and sacral portions of the spinal cord. Each system innervates the same organs but has contrary effects. TO PREVIOUS SLIDE

Sympathetic Division: fight or flight” response. UNIT B Chapter 12: Nervous System Section 12.4 Sympathetic Division: fight or flight” response. Increases heartbeat Dilates pupils Dilates airways Shunts blood away from digestive, urinary and reproductive areas Inhibits salivation Stimulates liver to release glucose uses the neurotransmitters epinephrine (adrenaline) and norepinephrine (NE) sympathetic division: division of the autonomic system that is active when an organism is under stress; activates the adrenal medulla to secrete the hormones epinephrine and norepinephrine Originates from Thoracolumbar Area “Feeling Together” TO PREVIOUS SLIDE

Sympathetic NS Sympathetic ganglia lie near spine stress response can feel all encompassing S for snake. rush before a big test, speech, or athletic event can attest, the effects of the sympathetic nervous system are quite pervasive. This is both because one preganglionic neuron synapses on multiple postganglionic neurons, amplifying the effect of the original synapse, and because the adrenal gland also releases norepinephrine (and the closely related hormone epinephrine) into the blood stream. preganglionic fibres short in sympathetic bc close to sc Post ganglionic are longer – farther to go

Parasympathetic Division: “rest and digest” response. UNIT B Chapter 12: Nervous System Section 12.4 Parasympathetic Division: “rest and digest” response. Constricts pupils Stimulates salivation Decreases heartbeat and blood pressure Constricts airways Stimulates gall bladder to release bile Stimulates digestive tract and urination Uses the neurotransmitter acetylcholine (ACh), which acts on different cells to add to the “rest and digest” response parasympathetic division: division of the autonomic system that is active under normal conditions; uses acetylcholine as a neurotransmitter Craniosacral origin TO PREVIOUS SLIDE

Parasympathetic Division preganglionic neurons have cell bodies located in the brainstem and in the sacral (toward the bottom) spinal cord ganglia often lie near or in effector, not urgent, communicate only with organs involved. “picnic” and “parasympathetic” both start with “p” Preganglionic fibers of the parasympathetic division arise from the base of the brain or from the sacral spinal cord. The preganglionic fiber is long, the postganglionic fiber is short, and ganglia lie close to the effector organ.

Autonomic Nervous System Sympathetic preganglionic fibers (left) arise from the cervical, thoracic, and lumbar portions of the spinal cord; parasympathetic preganglionic fibers (right) arise from the cranial and sacral portions of the spinal cord. Each system innervates the same organs but has contrary effects.

Which is false? The parasympathetic pathway is responsible for resting the body, while the sympathetic pathway is responsible for preparing for an emergency. Most preganglionic neurons in the sympathetic pathway originate in the spinal cord. Slowing of the heartbeat is a parasympathetic response. Parasympathetic neurons are responsible for releasing norepinephrine on the target organ, while sympathetic neurons are responsible for releasing acetylcholine.

Check your progress How many pairs of cranial nerves are there? How many can you list? How many pairs of spinal cord nerves are there? What are the divisions of the PNS? What is the Sympathetic NS responsible for? Compare effectors of Somatic and Autonomic Systems. PNS is divided into the somatic system and the autonomic system. Fight or flight

Patellar Reflex Activity The patellar reflex is an example of the monosynaptic reflex arc. There is no interneuron in the pathway leading to contraction of the quadriceps muscle. Instead the bipolar sensory neuron synapses directly on a motor neuron in the spinal cord.

Chapter Summary The nervous system consists of two types of cells: neurons and mesoglia. Neurons are specialized to carry nerve impulses. A nerve impulse is an electrochemical change that travels along the length of a neuron fiber. Transmission of signals between neurons is dependent on neurotransmitter molecules.

The central nervous system is made up of the spinal cord and the brain. The parts of the brain are specialized for particular functions. The cerebral cortex contains motor areas, sensory areas, and association areas that are in communication with each other. The cerebellum is responsible for maintaining posture; the brainstem houses reflexes for homeostasis.

The reticular formation contains fibers that arouse the brain when active and account for sleep when they are inactive. The limbic system contains specialized areas that are involved in higher mental functions and emotional responses. Long-term memory depends upon association areas that are in contact with the limbic system.

There are particular areas in the left hemisphere that are involved in language and speech. The peripheral nervous system contains nerves that conduct nerve impulses toward and away from the central nervous system. The autonomic nervous system has sympathetic and parasympathetic divisions with counteracting activities. Use of psychoactive drugs such as alcohol, nicotine, marijuana, cocaine, and heroin is detrimental to the body.