Intro Cns-pns Overview Slide1-26 1

Organization of Nervous System •Central Nervous System (CNS) A. Brain B. Spinal Cord

•Peripheral Nervous System (PNS) A. Spinal (Somatic) division = Voluntary B. Cranial = Special senses, muscles of head & neck C. Autonomic = Involunary 1. Sympathetic 2. Parasympathetic

SOME TERMS •Nerve = Collection of axons in periphery •Tract or Pathway = Grouped axons in CNS •Nucleus = CNS Neuronal group •Ganglion = PNS cell group

Neuroaxis • Forebrain – [lateral & third ventricles] – Telencephalon • [lateral ventricle] • cerebral cortex – lobes » sulci » gyri

• basal ganglia – corpus striatum (cerebral hemisphere) – subthalamic nucleus (diencephalon) – substantia nigra (midbrain)

Neuroaxis • Forebrain (cont.) – Telencephalon (cont.) • limibic system – – – – – – – –

limbic lobe amygaloid complex septal nuclei hippocampus mammillary bodies hypothalamus (see below) epithalamus (see below) assorted thalamic nuclei (see below)

Neuroaxis • Forebrain (cont.) – Diencephalon • thalamus • hypothalamus

Neuroaxis • Midbrain – [cerebral aqueduct] – Corpora Quadrigemina • superior colliculus • inferior colliculus

– Tegmentum (floor) – Tectum (roof) – Pineal Gland • seat of the soul

Neuroaxis • Hindbrain (Brainstem) – [fourth ventricle] – Metencephalon • Cerebellum – lobules – peduncles

• Pons

– Myelencephalon • Medulla (Oblongata)

-Brainstem contains functional centers assoc. w/ most of cranial nerves, long tract of afferent somatosensory info from body to forebrain, & efferent motor impulses for voluntary movements orig. in forebrain. -Damage: somatosensory and/or motor dysfunction & cranial nerve malfunction -diagnosed by cranial nerve malfunction. -frequently fatal: caudal vegetative functs.

Neuroaxis (& associated ventricles)

• Spinal Cord (31 vertebral segments) – – – – – –

[central cannal] Cervical (C1-C8) Thoracic (T1-T12) Lumbar (L1-L5) Sacral (S1-S5) Coccygeal (Co1)

-Relation between spinal cord levels and vertebral levels is clinically important. - Spinal cord lesions are localized according to the spinal cord segment. --Most spinal levels do not correspond to vertebral levels, however.

• Spinal Cord • Spinal Vertebrae

Neuroaxis • Peripheral Nervous System – spinal nerves and cranial nerves – somatic nervous system – autonomic nervous system • sympathetic nervous system (SNS) • parasympathetic nervous system (PSNS)

Terminology • AFFERENT = SENSORY information, conveyed TOWARD CNS • EFFERENT = MOTOR information, carried AWAY from CNS • EFFECTOR = Muscle or gland, carries out an action • RECEPTOR = Peripheral structure that captures and transduces stimulus information

Terminology (cont.) • INTERNEURON = small neuron with short processes, typically found in CNS • “RELAY” or “PROJECTION” NEURON = large neuron with long processes • COLUMN (FUNICULI) = vertical tracts, typically within spinal cord • COMMISSURE = horizontal axonal interconnections between nuclei in CNS • IPSILATERAL = same side • CONTRALATERAL = opposite side • DECUSSATION = sites where axon cross sides

Neurohistology • Chemical Neuroanatomy – when possible, neurotransmitters (NT) assoc w/ neurons and their projections will be discussed • better understand normal function & pathology – easier to understand affects of drugs on CNS

Preparation/Visualization of Brain Tissue • Fix brain – preserve it and make it easier to slice

• Section brain – so light can pass through it for microscopy

• Stain brain – so we can identify different structures and determine neurochemical phenotype of the cells

Preparation of Brain Tissue • Section brain – freeze brain to make it even harder and easier to cut – section with a microtome (‘that which slices small’) • vibratome

– sections need to be thin enough to permit light to pass through them (10-80 µm)

Preparation /Visualization of Brain Tissue

• Stain brain

– cell body stains (Nissl stains after Franz Nissl) • e.g., methylene blue – dye derived from distillation of coal tar

• e.g., cresyl violet, thionine, toludine blue • dyes are taken up by Nissl substances (RNA, DNA and assoc proteins in nucleus, ribosomes in cytoplasm)

Cresyl Violet Staining of Primate Brain

Preparation /Visualization of Brain Tissue • Golgi stains (after Camillo Golgi -won Nobel) • uses silver and causes a black reaction staining entire neuron and all processes • capricious staining of neurons – advantage because if all were stained it would be tangled mess – disadvantage because no one knows why some stain, others don’t

Golgi Staining of Cerebral Cortex

Preparation /Visualization of Brain Tissue • Stain brain (cont.) – fiber stains • e.g., hemotoxylin – have affinity for lipids (myelin sheath covering many axons

Hemotoxylin Staining of Rat Brain

Tract Tracing Techniques • This is how we know what is connected to what – rely on ability of neurons to take up tracer and transport them

• Anterograde Tract Tracing (away from cell body) – from dendrites to boutons

• Retrograde Tract Tracing (towards cell body) – from boutons to dendrites

• Transneuronal Tract Tracing (from neuron to neuron) – can be either anterograde or retrograde

Retrograde Tract Tracing • Horseradish peroxidase (HRP) – HRP is enzyme that splits peroxidase molecules making them insoluble salts (making them stay put) • readily taken up at synapse • can use pure or make even more likely to be taken up – conjugate it -- cholera toxin (bacterial toxin)or wheat germ agglutinin (WGA; lectin) – in vivo procedure – to make visible, react with benzine derivative (diaminobenzide tetrahydrochloride [DAB]) -- chromagen results

Anterograde Tract Tracing • Phaseolus vulagaris leukoagglutinin (PHAL) – plant lectin taken up by cell dendrites and transported to bouton – visualized by immunocytochemistry (ICC; see below) – advantage: detailed cell morphology, can go transsynaptically! – disadvantage: has to be iontophoretically applied, signal decreases with each synapse

Immunocytochemistry (ICC) • If you are interested in the distribution of a neurotransmitter, then ICC is appropriate • ICC works well in identifying neuropeptide transmitters because antibodies can be easily generated – simply, you use the ability of antibodies to attach to its antigen • then you make the antibody visible – most often, attaching a chromagen (coloring agent) to the non-binding part of the antibody produces too weak of a signal to visualize (‘direct visualization’) » you need to amplify signal by building on the binding of the antibody to the epitope of the antigen so you can attach more than one chromagen per bound antibody-antigen

In Situ Hybridization • ICC tells you the distribution of neurotransmitters (NTs) or their enzymes of synthesis – It does not tell you that the NTs are synthesized where they are located. •For example, serotonin is synthesized in midbrain (dorsal and median raphe) but projections go rostral to far reaches of forebrain •Thus, slices of forebrain show serotonin but not where it is made!

In Situ Hybridization • In situ hybridization tells you the where a neurotransmitters (NTs) It does not tell you that the NTs are distributed. •For example, in situ hybridization for serotonin would show midbrain location (dorsal and median raphe) but NOT the projections to rostral forebrain