Development and movement

DNA

• A gene is defined as a portion of a chromosome and is composed of deoxyribonucleic acid

  • segments of chromosomes are genes

  • this one is the long strand

  • holds the code of our genetics

RNA

• DNA serves as a model for the synthesis of ribonucleic acid (RNA

• RNA is a single strand chemical that can serve as a model for the synthesis of proteins

DNA → Proteins

• DNA (self replicating molecule) → RNA (copy of one strand of the DNA) → Protein (some become part of the body’s structure, others are enzymes that control the rate of chemical reactions)

  • each base determines one base of the RNA

  • a triplet of bases determines one amino acid

  • Process of transcription and translation

Transcription

• Enzyme unzips DNA and orders mRNA (messenger) bases according to DNA bases

• dictating the ordering of bases on the RNA strand

Translation

• in the nucleus the mRNA than leaves with that code and is read by ribosomes

• than bring in the right amino acid

• mRNA is read by ribosomes and tRNA sequences amino acids according to ordering of mRNA bases

Four paired bases construct the DNA molecule

• Adenine pairs with thymine

• Guanine pairs with cytosine

• needs to be truthful to the message why they pair

Transcription of RNA from DNA is determined by the ordering of DNA bases

• Adenine pairs with uracil → only on RNA

• Thymine pairs with adenine

• Guanine pairs with cytosine

Proteins

• determine the development of the body

• forming part of the structure of the body

• serving as enzymes

• antibodies

• messengers

• transport

Non-coding DNA

• most is non coding

  • providing instructions for how that process should occur

• promoters provide a site for transcription factors to attach and begin transcription

• enhancers enhances transcription of certain genes

• silencers repress transcription of certain genes

Mutation

• heritable change in DNA molecule

• evolution

• selfish gene→ goal of genetic code is the survival of the genetic code

• eventually become genetic code

Microduplication/microdeletion

part of a chromosome that might appear twice or not at all

Epigenetics

• A field that is concerned with changes in gene expression without the modification of the DNA sequence

• environment influence how that ball untwists

• some genes are active only at a certain point in ones life or a certain time of day

• changes gene expression are central to learning, memory, acclimatisation

• that wrapping or unwrapping is inheritable

Genes and behaviour

• Genes do not produce behaviours

• they produce proteins that increase the probability that a behaviour will develop under certain circumstances

• Can have an indirect effect

  • genes can alter your environment by producing behaviours or traits that alter how people in your environment react to you

Proliferation

• construction of new cells in the brain

• cells lining the inner surface of the neural tube divide or go through mitosis

• neurons and glia are eventually derived from these celss

• formation of neurons from non-neuronal cells is called neurogenesis

• neurogenesis has also been shown to happen in adults

  • olfactory for example

  • two main sites

    • hippocampus

    • subventricular zone

Migration

• Cells formed through mitosis migrate from the ventricular layer to their eventual destination

• Migration is aided by scaffolds

  • radial glia, blood vessels, immature neurons and chemical paths

  • help them climb path finding

• cells migrate in waves to form the layers of the cortex

  • cells of the outer layers arrive last

Differentiation

• The forming of the axon and dendrites that gives the neuron its distinctive shape

• the axon grows first either during migration or once it has reached its target and is followed by the development of the dendrites

• guided by gene expression and influences from neighbouring cells

Myelination

• the process by which glia produce the fatty sheath that covers the axons of some neurons

• Myelin speeds up the transmission of neural impulses

• first occurs in the spinal cord and then in the hindbrain, midbrain and forebrain

• Most intense period of myelination occurs after birth

Synaptogenesis

• the formation of the synapses between neurons

• occurs throughout the life as neurons are constantly forming new connections and discarding old ones

• slows significantly later in the lifetime, but synaptic plasticity remains

Pathfinding by axons

• axons must travel great distances across the brain to form correct connections

• Growing axons reach their target area by following chemical gradients

Competition among axons

• chemical pathways lead to approximately the right location

  • so it makes way to many connections then it needs

  • right neighbourhood wrong street

  • pruning

• post synaptic cells strengthen appropriate synapses

• others are eliminated

• made efficient through pruning

• the formation or elimination

Neuronal survival

• pre programmed to die apoptosis

• Nerve growth factor and brain derived neurotrophic factor are types of neurotrophies that promote the survival and growth of axons

  • stopping that cell death

• only those neurons forming accurate synapses receive neurotrophins

• involves both retrograde (post - pre) in the PNS and anterograde signalling in the CNS (pre-post)

The plastic brain

• Constantly changing

• The brain has the ability to reorganise itself in response to
  experience

  • Axons and dendrites continue to modify their structure
    and connections throughout the lifetime

  • Dendrites continually grow new spines

  • The gain and loss of spines indicates new connections,
    which relates to learning

Regrowth of Axons

• damaged axons typically do not regenerate in the CNS

• Scar tissue acts as a mechanical barrier to axon growth

  • inhibit at the right time we can regrowth

• Axon on the two sides of the cut pull apart

  • bridge can help

• glia cells release chemicals that inhibit axon growth

  • immature neurons to regrow in the

Axon sprouting

• Damage to axons leaves receptors vacant

• collateral axon sprouts from to fill these vacant spots

• this process is facilitated by the release of neurotrophins

• effectiveness of collateral sprouting can be varied

  • if different mixing up of messaging

What stages are involved in neural development

• Proliferation

• Migration

• Differentiation

• Myelination

• Synaptogenesis

Muscle fibres

• Muscles are composed of many individual fibres

  • each muscle fibre receives information from only one axon but a single axon may influence many muscle fibres

• Neuromuscular junction

  • synapse between a motor neuron and a muscle fibre

• release of acetylcholine causes the muscle to contract

The cerebral cortex

• the primary motor cortex is located in the precentral gyrus located in the frontal lobe

• Axons from the motor cortex project to the brainstem and the spinal cord

  • upper motor neurons

  • CNS

• motor neurons are then stimulated, controlling the lowe muscles

  • lower motor neurons

  • PNS

  • Motor homunculus

    • left control right

    • right controls left

Posterior parietal cortex

• keeps track of the position of the body relative to the workd

• damage to this area causes difficulty in coordinating visual stimuli with movement

• important for planning movement

Premotor cortex

• receives information about a target

• combines with the posterior parietal to form a visuomotor controller, aiding in accurate movement

• frontal parietal

Supplementary motor cortex

• organises sequence of movements in a specific order

• temporal structuring

Brain to the spinal cord

• messages from the brain project to the muscles via the medulla and spinal cord

  • cranial nerves are the exception

• Corticospinal tracts are paths from the cerebral cortex to
  the spinal cord

  • Two such tracts:

    • Lateral corticospinal tract

    • Medial corticospinal tract

Lateral corticospinal tract

• messages from right to left

• travels down the medulla and crosses there

Medial corticospinal tract

• crosses in the spinal cord

• basal ganglia involved

Planning a movement

• Posterior parietal cortex

• Premotor cortex

• Supplementary motor cortex

Refining movements

• Cerebellum

• basal ganglia

The cerebellum

• error detector and corrector

• a brain structure associated with balance and coordination

• detects and corrects erros in movement by receiving input from

  • vestibular system (where head is)

  • Proprioceptors (what you actually did)

  • Motor system

• Now you need to correct the error

  • direct impact send its own motor message

  • sends information up the motor cortex that you stuffed it up

Basal ganglia

• comprises of several structures

  • caudate nucleus (striatum)

  • putamen (striatum)

  • globus pallidus

• Important for spontaneous, self initiated behaviours

• involved in action selection

  • direct pathway

    • initiates movement

  • indirect pathway

    • inhibits movement