NERVOUS SYSTEM(神经组织) PPT

Reflexes: It is an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS. Reflex arc is the neuronal pathway by which a reflex occur. The reflex arc is the basic functional unit of the nervous system because it is the smallest, simplest pathway capable of receiving a stimulus and yielding a response. Components of reflex arc: (1) Sensory receptor, (2) Sensory neuron, (3) Interneurons, (4) Motor neuron and (5) Effector organ.
1. The central nervous system (CNS) consists of the brain and spinal cord, whereas the peripheral nervous system (PNS) consists of nerves and ganglia. 2. The sensory division of the PNS transmits action potentials to the CNS; the motor divisls away from the CNS. 3. The somatic motor nervous system innervates skeletal muscle and is mostly under voluntary control. The autonomic nervous system innervates cardiac muscle, smooth muscle, and glands and it is mostly under involuntary control. 4. The autonomic nervous system is divided into sympathetic, parasympathetic and enteric portions.
Neuron or Nerve Cell Receive stimuli and transmit action potentials to other neurons or effector organs. Parts include; 1. Cell body – consists of a single nucleus, rough ER, golgi apparatus and mitochondria and structures of the cell. 2. Dendrites – are the cytoplasmic extensions of the neuron’s cell body. It function to receive information from another neuron. 3. Axon – a long cell process of the neuron. It conducts action potentials away or towards the CNS.
Nervous tissue consists of white matter and gray matter. Gray matter forms the cortex and nuclei in the brain and ganglia in the PNS. White matter forms nerve tracts in the CNS and nerves in the PNS.
Some of the important Neurotransmitters of the nervous system: 1. Acetylcholine (Ach) – excitatory and inhibitory, located in the brain and spinal cord, nerve tracts, skeletal muscle junction (NMJ) and ANS. 2. Norepinephrine – excitatory and inhibitory, located in the brainstem, nerve tracts, brain and spinal cord. 3. Serotonin – generally inhibitory and located in the brainstem, nerve tracts, brain and spinal cord. 4. Dopamine – generally excitatory, located in brainstem, nerve tracts, and ANS.
The Resting Membrane Potential: Is the charge difference across the membrane of unstimulated cell (polarized cell). Na⁺ channels, and some but not all K⁺ channels are closed. Few K⁺ diffuse down their concentration gradient through the open K⁺ channels making the outside of the cell positively charged.
Action Potentials: An action potential occurs when the charge across the cell membrane is briefly reversed.
The Synapse: 1. The synapse is the point of contact between two neurons or between a neuron and some other cell (muscle or gland). 2. An action potential arriving at the synapse causes the release of a neurotransmitter (Ach) from the free synaptic terminal, which diffuses across the synaptic cleft and binds to the receptors of the postsynaptic membrane.
Neuroglia: 1. Astrocytes – star-shape, provide structural support of blood vessels and serve as blood-brain barrier. 2. Ependymal Cells – squamous epithelial-like that lines the ventricle of the brain, circulate CSF. 3. Microglia – small mobile cells that protects CNS from infection. Become phagocytic in response to inflammation. 4. Oligodendrocytes – surround several axons that form myelin sheaths and enclosed unmyelinated axons in the CNS. 5. Schwann Cells – single cell surrounding axons that form myelin sheaths and enclosed unmyelinated axons in the PNS.
Types of neurons: 1. Multipolar – several dendrites and one axon. Location is motor and CNS neuron. 2. Bipolar – one dendrite and an axon. Found in the eye and nose. 3. Unipolar – with single axon only. Located mostly on sensory neurons.
1. Sensory Input – Sensory receptors monitor numerous external ad internal stimuli that may be interpreted as touch, temperature, taste, smell, sound, blood pressure, and body position. Action potential travels from the sensory receptors to spinal cord and brain where they are interpreted. 2. Integration – The brain and spinal cord are the major organs for processing sensory input and initiating responses. 3. Homeostasis – This function depends on the ability of the nervous system to detect, interpret and respond to changes in internal and external condition. 4. Mental Activity – The brain is the center of mental activity such as consciousness, memory, and thinking. 5. Control of Muscles and Glands – Skeletal muscles contract only when stimulated by the nervous system. The nervous system also participate in controlling cardiac muscle, smooth muscle and many glands.