Download Fundamentals of Nervous System and Nervous Tissue

Fundamentals of Nervous System and Nervous Tissue
Chapter 12
Nervous System
The nervous system is the main system to communicate and coordinate body activities by sending electrical
impulses. Nervous system forms a communication network in whole body. Endocrine system communicates
through chemical messengers – hormones.
Brain
12 pairs of Cranial nerves arise from brain
(Part of PNS)
Spinal nerve cord
31 pairs of spinal nerves arise from spinal
nerve cord (Part of PNS)
Central NS
Afferent Division
Peripheral NS
Somatic sensory
Visceral sensory
Somatic NS
Efferent Division
Autonomic NS
Sympathetic
Parasympathetic
Neuron
A neuron has a cell body. Many smaller branched appendages are called Dendrites. Dendrites bring in information
(nerve impulse) to the cell body. A single longer appendage is called Axon. It takes information away from cell body.
It branches at the end into terminal knobs. A terminal knob secretes a chemical called Neurotransmitter in the gap
to the next neuron or muscle membrane.
3-types of neurons (on basis of function)
Specialized nerve cells are called Neurons.
Sensory neurons bring information from sense organs like eyes to CNS. Sensory = Affrent. Somatic Sensory =
coming from body wall - skin, muscles and joints; Visceral Sensroy = coming from internal organs - viscera
Motor neurons take information from CNS to effectors like muscles or glands. Motor = Effrent. Somatic Motor –
going to skeletal muscles and Visceral Motor – going to smooth or cardiac muscles.
Inter-neurons receive information from sensory neurons and integrate it, interpret the meaning and pass
instructions to motor neurons to act.
Neurons (on basis # of appendages)
Multipolar Neurons – many dendrites and 1 axon; most neurons in nervous system
Unipolar Neurons – 1 appendage, one end acts as dendrite and other end as axon, cell body attached to the middle
of appendage; sensory neuron in dorsal root ganglion of spinal nerve
Bipolar Neurons – 1 dendrite and 1 axon; neurons in middle layer of retina
Neuroglial Cells
Neuroglial Cells are non-conducting cells and have 4 kinds:
Astrocytes have many appendages, anchor neurons, form blood brain barrier, provide nourishment to neurons
Oligodendrocytes form myelin sheath around axons in CNS and Schwann cells form myelin sheath in PNS.
Microglial cells are phagocytes
Ependymal cells secrete cerebrospinal fluid.
1.
2.
3.
4.
CNS
Nucleus: Collection of cell bodies deep in brain
Tract: bundle of axons; tracts  Columns  pathways
Gray matter – mainly cell bodies; neural cortex,
centers, higher centers
White matter – mainly myelinated axons
PNS
Ganglion: Collection of cell bodies
Nerve: bundle of nerve fibers; may have 1-2 ganglia
Cranial nerves and spinal nerves
Sympathetic and Parasympathetic divisions of ANS
Important Terms
Polarization: + ions dominate outside nerve fiber and – ions dominate inside nerve fiber = resting potential
Depolarization: Na+ enter the nerve fiber, + ions dominate inside but – ions dominate outside nerve fiber
Repolarization returns back to original state, + dominate outside and – ions inside the nerve fiber.
Resting Potential
Resting Potential (- 70mV): is when a nerve fiber has more positive ions outside and more negative ions inside. It is
not conducting any electrical impulse. It is Polarization. Na+ - K+ pump maintains the resting potential by pumping
3Na+ out and bringing 2K+ in and consumes 1 ATP each time. Action Potential (+35mV) = nerve impulse travels as a
wave of depolarization from one segment of nerve fiber to next.
Meninges – CNS coverings
Meninges: Dura mater, Arachnoid and Pia Mater cover, just like brain, Spinal Cord.
Dura Mater = tough mother, outermost covering of brain and spinal cord
Arachnoid = vascular spidery middle covering
Pia mater = delicate mother, is in contact with brain
Outside dura mater epidural space is filled with fat and network of veins. Dura mater is not fused with bone
outside.
Spinal Nerve Cord
Spinal Cord: has a narrow central canal lined with ependyma and filled with cerebrospinal fluid. Gray matter lies
around central canal and has 2 anterior and 2 posterior extensions = Horns. The outer part is formed of white
matter and has ascending and descending tracts in it.
Ascending and descending pathways lie in spinal nerve cord (seen in T.S.).
Brain
Brain: has 6 main parts:
Fore-Brain
1. Cerebrum
2. Diencephalon
3. Mid-Brain
Hind Brain
4. Pons
5. Medulla
6. Cerebellum