Introduction to the Nervous System

Two Main Anatomical Parts. Central nervous system (CNS) – Brain – Spinal cord Peripheral nervous system (PNS) – Everything else Cranial Nerves Spinal Nerves

General Functions Sensory – gathering information – To monitor changes occurring inside and outside the body – Changes = stimuli Motor – A response to integrated stimuli – The response activates muscles or glands Integration – To process and interpret sensory input and decide if action is needed

Figure 7.1 Functional Classification Sensory (afferent) division – Nerve fibers that carry information to the central nervous system Motor (efferent) division – Nerve fibers that carry impulses away from the central nervous system Somatic nervous system = voluntary Autonomic nervous system = involuntary

Neuron processes: Axons – carry electrical impulses away from the neuron cell body Dendrites – Carry electrical impulses toward the neuron cell body Most, but not all neuron axons are myelinated. The myelin is highly lipid and provides electrical insulation.

Cells of the Nervous System A.Neuron = Functional Cell of the Nervous System B.Neuroglia (Neuroglial Cells, Glia, Glial Cells) 1)Microglia 2)Astrocyte 3)Ependymal 4)Oligodendrocyte 5)Schwann 6)Satellite Cells

1)Microglia – immune function, phagocytosis, debris removal 2)Astrocyte – control the chemical environment by forming the blood/brain barrier between capillaries and neurons 3)Ependymal – line cavities of brain and spinal cord, circulate CSF produced by choroid plexus 4)Oligodendrocyte – forms the myelin sheath in the CNS 5)Schwann Cells – forms the myelin sheath in the PNS 6)Satellite Cells – forms protective barrier around neuron cell bodies

Embryological Development A haploid sperm unites with a haploid egg A zygote is formed and mitotic divisions occur Morula  Blastula  3 Germs Layers Germs Layers = Mesoderm, Endoderm, Ectoderm Ectoderm gives rise to Notochord Anterior bulges of notochord differentiate into Forebrain, Midbrain & Hindbrain

Fig Pons, cerebellum Forebrain Midbrain Hindbrain Midbrain Forebrain Hindbrain Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon Spinal cord Cerebrum (includes cerebral cortex, white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, pineal gland) Midbrain Medulla oblongata Pituitary gland Cerebrum Cerebellum Central canal Diencephalon: Hypothalamus Thalamus Pineal gland (part of epithalamus) Brainstem: Midbrain Pons Medulla oblongata (c) Adult (b) Embryo at 5 weeks (a) Embryo at 1 month Brain Stem

Development Aspects of the Nervous System No more neurons are formed after birth, but growth and maturation continues for several years The brain reaches maximum weight as a young adult