Brain & Nervous System - 2


Anatomical Terms

From Carlson's crocodile

  • Neuraxis = imaginary line from nose-end to tail-end
  • Nose-end = rostral / anterior
  • Tail-end = caudal / posterior
  • Lateral = outer
  • Medial = inner
  • Dorsal = on top 
  • Ventral = underneath
1 of 12

Peripheral Nerves

  • Motor = efferent; bring responses from the brain to the muscles
  • Sensory = afferent; bring stimuli from the senses

The letter A comes before E in the alphabet - must have a stimulus before a response

  • Peripheral nerves join the CNS via 31 spinal nerves and 12 cranial nerves
  • White as they are coated in myelin
  • Motor fibres carry signals from fibres of the spinal cord to control muscles contractions and movements
  • Dorsal horn = incoming sensory fibres
  • Ventral horn = outgoing motor fibres
2 of 12


  • Organised in antagonistic pairs, e.g. during elbow joint flexion, biceps contract and triceps extend
  • Mechanical energy comes from the contraction of muscles, as the extension is passive
  • Action potential takes place in the motor neuron; meets at the neuromuscular junction 
  • Na flows into the muscle, allowing for the muscle equivalent of an action potential
  • Individual muscles are bundles of fibres
  • Myofibrils in muscle fibres are arranged in an interleaving way
  • Activation of the nicotinic receptors on the postsynaptic membrane causes end-plate potentials = the msucle equilvalent of EPSP
  • Ca2+ enters the muscle, triggering a chemical reaction that causes muscle contraction
  • The chemical reaction causes tension between the muscle fibres, which pulls them together and contracts the muscle
3 of 12


Monosynaptic Reflexes - Stretch

  • Single synapse in the reflex pathway
  • Sensory nerve endings in muscle spindles detect action potentials and are sensitive to muscles stretching
  • Activation of the stretch receptors triggers reflex muscle contraction

Polysynaptic Reflexes

  • Involves multiple synapses in the reflex pathway
  • Inhibitory interneurons mediate between sensory inputs and motor outputs
  • Involves reciprocal inhibition, e.g. when the extensor is stretched the flexor is inhibited
  • Sensory nerve endings on the intrafusal fibres of the muscle spindle generates action potentials that cause the extrafusal fibres to contract to oppose the stretch
4 of 12

PNS Afferent Groups

  • Four groups all served by the cranial nerves: visual, auditory, gustatory, olfactory and vestibular systems
  • Exteroceptive = receives external stimuli; allow us to detect tactile, thermal and the feeling of pain
  • Proprioceptors = receives stimuli from within the body, in particular it responds to position and movement
  • Interoceptive = receives stimuli from within the body, particularly from internal organs that makes us aware of some aspects of the state of our internal systems, e.g. the feeling of hunger
5 of 12

Types of Vestibular Sensor

Semicurcular Canals

  • 3 fluid-filled hoop-shaped structures in the inner ear
  • The ampullae contain hair cells
  • Detect angullar rotations of the head
  • Hair cells are embedded in a gel in the cupulla, which is in the ampullar swellings of the semicircular canals
  • Semicircular canals move when the head rotates, which deforms the cupulla, producing movement and action potentials in the hair cells

Vestibular Sacs

  • 2 different types of sacs: utricles and saccules
  • Fluid-filled and contain special sensors
  • Utricles - sensors on the floor
  • Saccules - sensors on the wall
  • Movement is created when the gel is dragged about by otoconia that are embedded in the gel
  • Otoconia = calcium carbonate crystals
6 of 12

Cranial Nerves & Vestibulo-Ocular Reflex

Cranial Nerves

  • Sensory inputs from the vestibular system enter the CNS via the 8th cranial nerve
  • This is the vestibulocochlear nerve
  • They are numbered according to their position
  • Vestibular nerves contact other areas of the brain, such as the thalamus

Vestibulo-Ocular Reflex

  • When the head rotates the fluid in the semi-circular canal rotates relative to its walls 
  • The retinal image of the target is displaced
  • The deflection of the hair cilia leads to action potentials
  • The oculomotor control systemsrotate the eye in the opposite direction to the head movement
  • Compensatory eye movement keeps a steady retinal image
7 of 12


  • Maintains homeostasis - majority of processes are unconscious
  • Sympathetic and parasympathetic = generally antagonistic
  • Pre and post ganglionic neurons between the CNS and the target
  • Sympathetic = short pre-ganglionic fibres
  • Parasympathetic = long pre-ganglionic fibres
  • All the sympathetic pathways pass through the sympathetic ganglion chain 


  • Organs receive input from the sympathetic and parasympathetic systems so that they are in a state of autonomic balance
  • E.g. sympathetic = increases heart rate and dilates pupil; parasympathetic = decreases heart rate and constricts pupil
8 of 12

CNS - Spinal Cord

Efferent / Motor

  • Receives sensory afferents from the body, controls movement and carries most of the sympathetic and parasympathetic outputs
  • Two types of tracts - lateral (outer) and ventromedial (inner)
  • Lateral - controls movement
  • Ventromedial - controls flexor and extenser muscles and posture

Afferent / Sensory

  • Sesnsory pathways from the skin and muscles to the somatosensory cortex are separate from the pathways that carry visual, auditory, olfactory, vestibular and gustatory info
  • Two types of pathways - spinothalamic tract and dorsal colum system
  • Spinothalamic tract - carries info regarding pain and temperature
  • Dorsal column system - carries info about touch
  • Both involve three neurons
9 of 12

Brain Development

  • At 20 days, the foetus cells begin to thicken; formation of neural plate begins at the fold, forming a neural groove
  • At 24 days, a tubular shape has developed which later forms the base of the brain
  • A developed human brain weighs around 1.4 kilos - 2-3% of our body weight
  • The rostral neural tube develops into three parts: forebrain, midbrain and hindbrain


  • Important in controlling sleep, movement (e.g. standing, walking) and arousal
  • Also involved in Pavlovian conditioning of the eyeblink reflex


  • Dorsal surface supports parts involved in visual and auditory systems
  • Hindbrain and midbrain make up the brain stem
10 of 12

Ventricular System & Forebrain

Ventricular System

  • Series of fluid-filled chambers that wrap around the brain to provide protection
  • Also provides nutrients and removes waste products


  • Thalamus = largest part of posterior part of forebrain (diencephalon)
  • Thalamic nuclei divided into lateral, medial, anterior, intralaminar and reticular groups
  • Lateral group contains part of visual and auditory pathways
  • Hypothalamus controls endocrine hormonal system and influences the ANS
  • Limbic system linked to controlling emotion and the hypothalamus
  • Amygdala involved in fear responses
  • Hippocampus located in temporal lobe and plays a part in explicit memory
11 of 12

Cortex Development & Coverings

Cortex Development

  • Develops by the outward movement of cells from the ventricular zone of the neural tube
  • Neural tube = hollow
  • This site of cell development is for the cells which eventually make up the cortex
  • Six waves of development
  • Cells that develop first make up the outside of the cortex
  • Once developed, cells form connections with other cortical cells and send out projections to other parts of the brain


  • CNS is protected by skull (bone), spinal column and CSF (fluid)
  • Three protective layers between the skull and brain/spinal cord: dura matter, arachnoid membrane and pia matter
  • CSF is circulates continuously - is reabsorbed and so constantly refreshed
12 of 12


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes and structure resources »