Counseling/Anatomy of the Brain and Neurosystem

Central nervous system, or CNS

• skull
• spine

Peripheral nervous system, or PNS

• Outside skull and spine
• Two divisions, external and internal

PNS nerves project from spinal cord to organs (with exceptions)

Somatic nervous system (SNS)

Relates to external environment

nerves

• afferent -- sensory signals from:
  • skin
  • skeletal muscles
  • joints
  • eye, ears

• efferent -- motor signals to:
  • skeletal muscles

Autonomic nervous system (ANS)

Regulates internal environment

nerves

Afferent and Efferent

afferent nerves

• carry sensory signals from internal organs to CNS

efferent nerves

• carry motor signals from CNS to organs

two kinds:

1. sympathetic
2. parasympathetic

functions:

• each organ, or autonomic target, receives opposing sympathetic and parasympathetic input
• organ is controlled by level of sympathetic and parasympathetic activity

sympathetic

• arousal
• threatening situations
  • stimulate
  • organize
  • mobilize

parasympathetic

• relaxation
• conserve energy

location:

• sympathetic project from CNS to lumbar and thoratic (chest) regions
• parasympathetic project from CNS to brain and sacral (lower back) regions

nature: both have two stage neural paths that synapse on other neurons between organs and spinal cord

• sympathetic synapse farther from organs
• parasympathetic synapse nearer to organs

cranial nerves

12 parasympathetic cranial nerves project from brain

purely sensory:

• olafactory
• optic

sensory and motor:

• vagus nerves -- gut

disease diagnosis:

• disruption of nerves can pinpoint tumors and other pathologies

CNS protection

CNS tissue covering

• meninges -- three membranes that cover CNS (meninx, singular)

cerebrospinal fluid (CSF) -- CNS cushion and physical support, single connected reservoir

• sub-arachnoid space -- between inner and middle meninges
• central canal -- runs length of spinal cord
• ventricles -- four large internal chambers
  • 2 lateral
  • 3rd and 4th vertical

blood brain barrier:

• tightly-packed blood vessels
• filters passage of molecules by type
• filters differently by location (sex hormones)

Neurons

electrochemical signals:

• reception
• conduction
• transmission

external

• membrane
• dendrites
• axon
  • axon hillock
• myelin
• nodes of ranveir
• buttons -- ends of axons
• synapses

internal

common to all cells:

• endoplasmic reticulum -- folded membranes
  • ribosomes (rough area) -- synthesis of proteins
  • smooth -- synthesis of fats (without ribosomes)
• cytoplasm -- clear internal fluid
• golgi complex -- packages molecules in vesticules (makes vesticules?)
• micro tubules -- transport tubes

neural transmission

• synaptic vesticules -- store neurotransmitters
• neurotransmitters -- chemicals that influence post-synaptic cells

cell membrane

• lipid bilayer -- membrane surfaces, inside and out
• thru-membrane passages
  • channel proteins -- allow specific molecules to pass
  • signal proteins -- transfer signal from outside to inside when molecule binds on outside

classes of neurons

• multipolar (most common) -- two or more processes (axons/dendrites) extending from body
• unipolar -- one process extending from body that can divide into multiple extentions
• bipolar -- two processes extending from body
• interneurons -- short, or no, axons conduct signals within a single brain structure

gross neural structures

nuclei -- clusters of cell bodies in CNS ganglia -- clusters of axons in PNS

bundles of axons:

• tracts in CNS
• nerves in PNS

glial cells

90% of brain cells, primarily support neurons

• oligodendrocytes -- CNS
  • create myelin sheaths around
  • wrap around axons in CNS sending out extensions (does it stay connected, or release myelin?)
• schwann cells -- PNS
  • create myelin sheaths
  • creates only one sheath and can regenerate myelin
• astrocytes -- some in blood barrier system
  • transport chemicals from blood to neuron bodies
  • extensions cover blood vessels
  • connect to neuron bodies
• micoglia -- respond to injury or disease
  • engulf cellular debris
  • trigger inflammatory responses

Directional references

axis

anterior / posterior

• front / back
• front of brain, but upwards in body

dorsal / ventral

• top / bottom
• dorsal is top of brain, but back of body
• ventral is bottom of brain, but front of body

superior -- top

inferior -- bottom

in / out

• medial -- towards midline
• lateral -- away from midline towards lateral, or outside, surfaces

far / close

distal -- far from CNS proximal -- close to CNS

sections

• sagittal -- vertically divides left and right
• frontal -- vertically divides front and back
• horizontal -- divides top and bottom
• cross section -- cut across nerve or spinal cord

Spinal cord

gray matter

• core
• H-shaped
• cell bodies
• unmyelated neurons
• horns
  • dorsal
  • ventral

white matter

• surrounding
• myelated axons (white lipid)

attached nerves

• 31 pairs of nerves attached
  • left and right (bundles of axons)
• axons go to ventral and dorsal horns
• sensory neurons (unipolar) go to dorsal horns with bodies outside in nerve bundle forming dorsal root ganglia
• motor axons emerge from ventral with neuron bodies in horn
  • somatic project to the skeletal system
  • autonomic connect to ganglia (clusters of cell bodies) that synapse on neurons that connect to organs

Brain

5 divisions from top to bottom:

• telenephalon
• diencephalon
• mesencephalon
• metencephalon
• myenlencephalon (medulla)

spinal cord is beneath myenlencephalon

From 3 sections:

• forebrain, telenephalon and diencephalon
• midbrain, mesencephalon
• hindbrain, metencephalon and myenlencephalon

myenlencephalon

• tracts for signals between brain and body
• also called medulla

rectiliniar formation

• network of 100 tiny nuclei within central core of brain stem

spans:

• posterior boundary of myelencephalon (bottom of medulla)
• anterior boundary of mesencephalon (top of midbrain)

rectiliniar activation system:

• sleep
• attention
• movement
• muscle tone maintenance
• heart beat
• circulation
• respiratory reflexes

diencephalon

thalamus and hypothalmus

thalamus

• 2 lobes joined by massa intermedia
• top of brainstem
• on top of third ventricle

• pairs of nuclei that project to cortex (most)

• sensory relay nuclei (many)
  • receive signals from sensory receptors
  • process signals
  • transmit to specific areas of sensory cortex

lateral geniculate nuclei visual sensory relay nuclei

hypothalamus

• below (hypo) thalamus
• regulation of motivated behaviors
  • regulates release of hormones from pituitary gland (attached below/front)

attached structures:

• pituitary gland
• optic chasm
  • decussate or contralateral (cross over to other side)
  • ipsilateral (staying on same side)
• mammilary bodies
  • behind pituitary

telencephalon

• largest division
• voluntary movement initiation
• interprets (processes) sensory movement
• mediates complex cognitive processes
  • learning
  • speaking
  • problem solving

cerebral cortex

also cortex

• layer of tissue
• convoluted, or furrowed
  • • increase amount of cerebral cortex from same tissue mass

convolutions:

• fissures, large furrows
• singular suclcus, small furrows
• gyri, ridges between fissures

longitudinal fissure:

• separates hemispheres
• largest fissure
• connections between hemispheres (tracts)
  • cerebral commisures
  • largest, corpus callosum
  • minimal number of tracts

lateral fissure: major horizontal fissure

four lobes divided by horizontal and latteral fissures:

• frontal
• parietal
• temporal
• occipital

major gyri:

• precentral, contain motor cortex
• postcentral, somatosensory cortex (body sensation)
• superior temporal gyri, auditory cortex

neocortex:

• 6-layered cortex
• 90% of cortex
• evolutionary recent
• numbered I through VI

two types of neurons:

pyramidal

• multipolar
• large
• apex runs to surface of cortex
• long axon

stellate

• interneurons
• star-shaped
• small with short or no axon

non-neo cortex

• fewer layers

• hippocampus
  • memory
  • medial edge of cerebral cortex
  • curves back on itself in medial temporal lobe

• cingulate cortex

limbic system

circuit of mid-line structures in brain

motivated behaviors

• fleeing
• feeding
• fighting
• sex

members:

• hippocampus
• cingulate cortex

sub-cortical

• mamillary bodies
• amygdala
• fornix
• septum

basal ganglia

• voluntary movement
• sub-cortial structures

members:

• amygdala
• caudate (circle)
• putamen (within circle, straitum with caudate)
• globus pallidus