Biological Bases of Behaviour. Lecture 10: Movement.

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Biological Bases of Behaviour. Lecture 10
Movement.
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Learning Outcomes.

• By the end of this lecture you should be able to
• 1. Outline the key anatomical components of the
  movement system.
• 2. Describe the effects of damage to each of the
  components.
• 3. Explain how the various components of the
  system are organised.

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Anatomy of Movement.

• The motor system can be divided into a number of
  subsystems
• 1. Muscles
• 2. Spinal cord
• 3. Cerebellum
• 4. Reticular formation
• 5. Basal ganglia
• 6. Cortex
• They share many interconnections with each other.
  
• Remember that each hemisphere of the brain
  controls the trunk of the body on the same side,
  and the arms and legs of the opposite side.

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1. Muscles.

• A part of the body that can move is called an
  effector.
• A distal effector is far from the body centre
  (hands, feet).
• A proximal effector is centrally located (waist,
  neck, eyes).
• Muscles are attached to the skeleton at joints
  and can only move in one direction.
• In order to make an arm extend and flex, it
  requires a pair of muscles working in opposition
  enabling the effector to flex and extend.
• E.g activating the biceps flexes the forearm,
  activating the triceps extends the forearm.

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Muscle Action.
Tricep relaxes
Bicep contracts
Bicep relaxes
Tricep contracts
Kalat (2001) p225
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Muscles (continued).

• A neuromuscular junction is a synapse where a
  motor neuron synapses with a muscle fibre, all
  such connections are excitatory and release
  acetylcholine.
• The muscles interact with the nervous system via
  the alpha motor neurons which originate in the
  ventral section of the spinal cord.
• In vertebrates there are three types of muscles
• Smooth muscles control movements of internal
  organs.
• Skeletal muscles control the movement of the
  body parts.
• Cardiac muscles control the heart.

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Muscle Control.

• Muscles are controlled by proprioceptors which
  are specialised receptors sensitive to the
  position and movement of the body.
• They detect the stretch and tension of a muscle
  and send messages to the spinal cord to enable it
  to adjust its signals to the muscles. There are
  two main types
• a) Muscle spindle a stretch receptor lying
  parallel to the muscle. When stretched it sends a
  message to a motor neuron in the spinal cord
  which in turn relays a message to the muscle
  causing a contraction. E.g the knee-jerk reflex.
• B) Golgi tendon organ located in the tendons at
  both ends of the muscle. It acts as a brake
  against excessive contractions by inhibiting the
  motor neurons in the spinal cord.

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Proprioceptors
Spinal cord
Motor neurons
Sensory neurons
Muscle
Muscle spindle
Golgi tendon organ
Kalat (2001) p227
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Disorders of the Motor Neurons.

• a) Myasthenia Gravis The immune system
  progressively attacks acetylcholine at the
  neuromuscular junction.
• This leads to progressive muscle weakness and
  rapid fatigue apparent after short periods of
  exercise.
• Drugs such as Physostigmine (an acetylcholine
  agonist) alleviate the symptoms.
• b) Multiple Sclerosis A common diseases
  characterised by the loss of myelin surrounding
  sensory and motor neurons.
• The myelin loss is patchy but a sclerotic plaque
  forms which severely impairs the functioning of
  the neuron.
• Onset is rapid with first symptoms being limb
  weakness, disorders of vision, tremors, vertigo.
• There is no treatment as yet.

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2. Spinal Cord.

• This cord distributes motor fibres to the
  effectors and collects sensory information to be
  passed to the brain.
• It is protected by 24 vertebrae.
• Small bundles of fibres emerge from the spinal
  cord, groups of these bundles fuse to form the
  dorsal and ventral roots which form the spinal
  nerves.

Dorsal roots
Ventral roots
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Effects of Damage to the Spinal Cord.

• Dorsal root damage normal movement is possible
  but sensory information is lost.
• Ventral root damage sensory information is
  received but movement is lost.
• Paraplegia Lower limbs are paralysed.
• Hemiplegia One side of the body is paralysed.
• Quadraplegia All four limbs and the trunk of the
  body are paralysed - usually caused by a broken
  neck.

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3. Cerebellum.

• This structure contains more neurons than the
  rest of the brain.
• It receives input from the spinal cord, the
  sensory systems, and from the cortex.
• It co-ordinates muscle activity, maintains
  balance, and plays a role in motor skill
  learning.

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Effects of Cerebellum Damage.

• Cerebral palsy Caused by lack of oxygen during
  the birth process.
• Movements becomes jerky, erratic, and
  uncoordinated, and movement sequencing becomes
  problematic.
• Also affected is speech, control of eye
  movements, writing and even simple alternating
  movements (such as clapping) become difficult.
• Alcohol intoxication It is one of the first
  areas of the brain to show the effects of alcohol
  intoxication.
• Symptoms are slurred speech, clumsy motor
  control, loss of balance, and inaccurate eye
  movements.

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4. Basal Ganglia.

• This comprises a set of interconnected nuclei in
  the forebrain which includes
• Caudate nucleus.
• Globus pallidus.
• Substantia nigra.
• Subthalamic nucleus.
• Putamen.
• The caudate nucleus and putamen receive sensory
  input from the thalamus and cortex, while the
  globus pallidus sends information to the primary
  motor cortex via the thalamus.

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Basal Ganglia.
amygdala
Substantia nigra
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Effects of Damage to the Basal Ganglia

• The basal ganglia have rich connections to the
  cerebral cortex and subcortical nuclei.
• They not only contribute to movement but they
  also influence cognitive functioning (though
  exactly how is not yet known).
• Damage to them produces a variety of changes in
  movement though two main problems emerge
• Akinesia (an absence of spontaneous movement) as
  seen in Parkinsons disease.
• Hyperkinesia (rapid involuntary movements) as
  seen in Huntingtons disease.

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5. Reticular Formation.

• This consists of a large number of nuclei located
  in the core of the medulla, pons and midbrain
  which principally control muscle tone and
  posture.
• Nuclei in the pons and medulla also control
  automatic movements such as vomiting, coughing
  and sneezing.
• Other motor functions of this structure are still
  being discovered but it also seems to play a role
  in locomotion though it does not have a direct
  connection to the spinal cord.

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6. Cerebral Cortex.

• The role of certain regions of the cerebral
  cortex in motor activity was discovered in 1870
  by Fritsch Hitzig.
• They electrically stimulated the exposed cortex
  of a dog and observed the co-ordinated movements
  of several muscles.
• The cerebral cortex does not connect directly to
  the muscles, but sends axons to the medulla and
  spinal cord, which in turn send axons to the
  muscles.
• So, unlike the spinal cord, the cortex is
  responsible for the overall planning of movements
  and not individual muscle contractions.
• It is not responsible for automatic and
  involuntary movements e.g coughing, laughing,
  sneezing and gagging.

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Cortical Motor Regions

• There are several cortical regions controlling
  various aspects of movement
• Primary motor cortex The main movement
  processing region, within which separate areas
  control different parts of the body.
• Premotor cortex Active during the preparations
  before a movement has begun (motor planning).
• Supplementary motor area Active during the
  preparation before a rapid series of voluntary
  movements.
• Prefrontal cortex Responds mostly to sensory
  signals that lead to movement.
• Somatosensory cortex Primary receiving area for
  touch and and is closely connected with the motor
  processing regions and spinal cord.

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Cerebral Cortex (continued).
Primary motor cortex
Primary somatosensory cortex
Central sulcus
Supplementary motor cortex
Premotor cortex
Prefrontal cortex
Kalat (2001) p232
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Effects of Damage to the Cerebral Cortex.

• By investigating patients with various types of
  brain damage we can see how the various
  components of motor performance may be affected.
  Examples
• Lesions to primary motor cortex (ie from a
  stroke) result in loss of voluntary movements on
  the contralateral (opposite) side of the body.
• Apraxia is the specific loss of the ability to
  plan and correctly perform co-ordinated motor
  skills, mainly as a result of damage to the
  supplementary motor area.
• Patients can move muscles, and walk on command
  but can no longer link gestures to a coherent
  act, or to recognise the appropriate use of an
  object even though they can recognise what an
  object is.

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Cortical Control of Movement.

• The cortex can regulate the activity of spinal
  neurons in direct and indirect ways
• a) Pyramidal system Consists mainly of axons
  from primary motor cortex and adjacent areas.
• These axons descend to the medulla where they
  decussate (cross over) in distinctive swellings
  called pyramids.
• The fibres then split as they enter the spinal
  cord, forming the
• Dorsolateral tract controls peripheral body
  movements (fingers, toes etc).
• Ventromedial tract controls movements at the
  midline (back and neck etc).
• This system is also referred to as the
  corticospinal tract.

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Cortical Control of Movement (continued).

• b) Extrapyramidal system This consists of all
  the movement-controlling areas other than the
  pyramidal system.
• Axons from the basal ganglia and diffuse areas of
  the cortex converge onto the red nucleus, the
  reticular formation, and the vestibular nucleus.
• Each of these areas then sends axons to the
  medulla and spinal cord.

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Hierarchy of Movement Control.

• Most movements rely on both pyramidal and
  extrapyramidal systems, and on dorsomedial and
  ventrolateral tracts. There is a hierarchy of
  motor control
• Lowest level The spinal cord which provides a
  point of contact between the nervous system and
  the muscles, and also controls reflexive
  movements.
• Middle level The motor cortex and brainstem
  structures (plus the the cerebellum and basal
  ganglia) translate a specific set of action goals
  into movement via their communication with the
  spinal cord.
• Highest level Premotor and cortical association
  areas which are concerned with the planning and
  organisation of movement based on current
  perceptual information and previous experience.

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Bibliography.

• Carlson, N.R. (1994). Physiology of Behaviour.
• Gazzaniga, M.S., Ivry, R.B., Mangun, G.R.
  (1998). Cognitive Neuroscience.
• Kalat, J.W. (1995). Biological Psychology.