CHAPTER 48 NERVOUS SYSTEMS Section B Vertebrate Nervous

CHAPTER 48 NERVOUS SYSTEMS Section B: Vertebrate Nervous Systems Dr. Hesham Sharaf

Nerve impulses propagate ﺗﻗﻯ themselves along an axon • The action potential is repeatedly regenerated along the length of the axon. – An action potential achieved at one region of the membrane is sufficient to depolarize a neighboring region above threshold. Thus triggering a new action potential. The refractory period assures that impulse conduction is unidirectional. • Saltatory conduction ﺍﻟﺘﻮﺻﻴﻞ ﺍﻟﻘﻔﺎﺯ. – In myelinated neurons only, the unmyelinated regions of the axon depolarize. Thus, the impulse moves faster than in unmyelinated neurons. Fig. 48. 10 & 48. 11, Page 1032 Dr. Hesham Sharaf Un 7, Ch 48

Cellular communication There are two types of communication between cells: • Electrical Synapses. – Action potentials travels directly from the presynaptic to the postsynaptic cells via gap junctions ( ﺃﻤﺎﻛﻦ ﺍﻹﺗﺼﺎﻝ less common). • Read legend of figure Chemical Synapses. 48. 12, Page 1033 – More common than electrical synapses. – Postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl- via synaptic cleft. – Depending on which gates open the postsynaptic neuron can Dr. Hesham Sharaf depolarize or hyperpolarize. Un 7 Ch 44 Fig. 48. 12, Page 1033

The same neurotransmitter can produce different effects on different types of cells v Acetylcholine. – Excitatory ﻣﺤﻔﺰ to skeletal muscle. – Inhibitory ﻣﺜﺒﻂ to cardiac muscle. – Secreted by the CNS, PNS, and at vertebrate neuromuscular junctions. v Biogenic Amines. – Epinephrine and norepinephrine. • Can have excitatory or inhibitory effects. • Secreted by the CNS and PNS. • Secreted by the adrenal glands. Synaptic terminal communication Dr. Hesham Sharaf Nerve i mp u l se

Vertebrate nervous systems have central and peripheral components • Central nervous system (CNS). a) b) c) • Brain and spinal cord. – Both contain fluid-filled spaces which contain cerebrospinal fluid (CSF). – The central canal of the spinal cord is continuous with the ventricles of the brain. White matter is composed of bundles of myelinated axons. Gray matter consists of unmyelinated axons. Peripheral nervous system (PNS). – Everything outside the CNS. a) Cranial nerves ( ﺃﻌﺼﺎﺏ ﺍﻟﺠﻤﺠﻤﺔ 12 pairs): that originate in the brain and innervate the head and upper body. Spinal nerves ( ﺃﻌﺼﺎﺏ ﺷﻮﻛﻴﺔ 31 pairs): that originate in the spinal cord and innervate the entire body. Ganglia associated with the cranial and spinal nerves. b) c) Dr. Hesham Sharaf

ﺟﺎﺭ ﺍﻟﺴﻤﺒﺜﺎﻭﻯ • A closer look at the (often antagonistic) divisions of the autonomic nervous system (ANS). Dr. Hesham Sharaf Fig. 48. 18, Page 1041 ﺍﻟﺴﻤﺒﺜﺎﻭﻯ